Volume: 19 ; Start Page: 92 ; End Page: 9

Blackman, M. W.

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9 Psyche [June43, there is no mention of Actias rossi. Neither is it mentioned inthe "synopsis" on page 78, where only luna is listed.Another variety of Tropcea luna, is Walker’s dictynna, Cat. Lep.Het. Brit. Mus. VI, 164. The description is as follows: "Yel-lowish green. Head and fore part of the thorax whitish. Thoraxwith a broad purple band in front. Wings with an exterior slen-der incomplete pale brown band, which is most incomplete on thehind wings. Fore wings with a purple costal stripe, from whencea short branch proceeds to the vitreous ocellus; the latter is trans-versely elliptical and is bordered with brown, tawny, black, blueand black on the inner side, and with lilac, red, luteous and fer-ruginous on the outer side. Hind wings with a round ocellus,larger than that of the fore wings, but with the like disposition ofcolours; tails rather shorter than the breadth of the hind wings.Length of the body 1 lines; of the wings 5 lines."This species much resembles T. luna, but may be distinguishedby the band on the wings, by the not empurpled exterior border,by the fore wings, which have a less oblique and more straightexterior border, and by the hind wings, which have shorter tails."Variety dictynna is to be found more abundantly in the South-ern United States.ON A SUPERNUMERARY MEDIAN OCELLUS IN MEL-ANOPLUS FEMUR--RUBRUM.B M. W. BXCKMAN,Zoological Laboratory, Syracuse University.In conducting laboratory work upon invertebrate forms, theteacher oten has opportunities for observing interesting abnor-malities of various organs both internal and external. Theseunusual structures are as a general thing very apparently due toinjuries followed by a more or less successful attempt at repair orregeneration. Occasionally, however, anamolies occur which seemhardly to fit in with such an explanation and which must be classedas congenital. It is the belief of the writer that such cases shouldbe reported even though no adequate explanation of the reasonfor the abnormality can be offered.In insects the ocelli are usually present to the number of three--1911] Blackman--Supernumerary Median Ocellus 93two lateral ones, lying more dorsally, and a single median one.This arrangement is subject to considerable variation and eventhe number is not constant for the entire class. There may beonly two present (Lepidoptera, etc.) or only one, and indeed in anumber of cases (Dermaptera, Locustide, Coleoptera, some Hom-optera, and some Lepidoptera), the ocelli may be entirely absentin the adult. So far as the writer knows the ocelli are never morenumerous than three except in immature forms, degenerate para-sitic forms, and in certain of the very lowest insects in which groupsof ocelli take the place of the compound eyes. In the pupal stageof Bombus the median ocellus, according to Packard possesses "adouble shape, being broad, transversely ovate and not round likethe two others, as if resulting from the fusion of what were origi-nally two distinct ocelli." In accordance with this we might ex-pect to find a pair of median ocelli or at least transversely ovateone in the adult or nymphal stages of lower insects. Such, how-ever, is not the case except possibly in other members of the orderItymenoptera where as will be mentioned later the structure ofthe nervous connections are such that we might expect occasionaldouble median ocelli in the immature stages and possibly even inthe adult.The normal number of ocelli in the short horned grasshoppersis three, arranged in a triangle, the two dorsal ones being lateraland near the inner margin of the compound eye, while the ventralocellus is median in position ventral to t.he antennae. In a num-ber of years experience with grasshoppers in laboratory work withlarge classes the writer has never seen any variation in the numberor relative position of these ocelli. Last fall, however, an adultfemale specimen of Melanoplus femur-rubrum was brought to meby one of my students which possessed two median ocelli insteadof the ordinary single one. As I had never seen or heard of suchan anamoly, the specimen was preserved for further study.The accompanying photograph reproduced at a magnificationof about five diameters shows the conditions better than would alengthy description. The two median .ocelli will be llainly seenplaced symmetrically one on each side of the median line. Eachis approximately circular and apparently perfect in every respect.Each one as far as could be observed is but slightly smaller than1Packard A. S. Text Book of Entomology Macmillan Co., New York (1898).94 Psyche [Junethe single ocellus usually is. The two are entirely distinct, eachbeing set in a slight depression with the intervening distance,greater than the diameter of each ocellus. The lateral ocelli, oneat the inner upper margin of each compound eye are both presentand both normal. Unfortunately, due to lack in depth of focusof the lens used, these do not show in the photograph.Believing it would be interesting to know the nature of the ocel-lar nerve and its relation to the brain, the head was removed and.Fig. 1. Face view of Melanoplus femur-rubrum showingthe supernumerary median ocellus.placed in weakened solution of eau de Labaraque for twenty-fourhours to soften the chitin. It was then dehydrated and embeddedin paraffin in the usual way and serial sagittal sections tenmicra thick were prepared. These sections were used as a basisfor a reconstruction of the ocelli and ocellar nerve.In the normal grasshopper as was shown many years ago bythe beautiful dissections and drawings of Burgess, the nerve to,the median ocellus in M. femur-rubrum arises independently asBurgess, E. In the article "The brain of the Locust" by A. S. Packard. 2d rept.U. S. Entom. Com. 1880.1912] Blackman--Supernumerary Median Ocellus 95a single strand from the central brain mass in the median line andpasses directly to the ocellus without branching. The writer wasinterested to know whether in this abnormal case the nerve sup-ply would take the form of two entirely separate nerves or wouldarise as a single nerve and later branch. A graphic reconstruc-tion made by the well known method is shown in Fig. . Thenerve arises as a single one ust as in the normal head and isdivided only in the last third ot its course. As would be expectedfrom the distance between the ocellar lenses s seen in lig. 1, thereis a complete division of the nerve termination, the two retinalcups baing entirely separate.,02.ig. . Graphic reconstruction of the median oeellar nerve, showing its originas a single strand and its later bifurcation. X 0.ig. . Sketeh of a portion of a median sagittal section of the head, showingthe origin of the nerve from the brain, and the oeellar eup and lens. he fixationis sueh as to be of value only in showing the general relations. N 0.The entire length of the undivided portion of the nerve is notshown in Fig. on account o a looping (apparent in Fig. 3) justafter its exit from the brain. This would of course result in aconsiderable fore-shortening in a graphic reconstruction. Fig. 3represents a sketch of a portion of a median sagittal section of thehead showing the proximal half of the ocellar nerve and also a sec-tion of the ocelli. The histological fixation, due to the fact thatthe material was preserved with a large, number of other speci-mens or ordinary dissecting purposes and perhaps was later whollyor partially dried, is not such as to show finer details either in brain,96 Psyche [Junenerve, or ocellus but is sufficiently good to show the relations ofthe various parts.It would appear to be true that in the grasshopper the nerve ofthe median oeellus is primarily a single nerve bundle. In otherinsects, notably Hymenoptera, it has been shown that the nervesupply of the single median oeellus arises as two strands whichlater fuse, (Viallanes, Janet) and ends in the single sensory cup.In such eases each half of the median oeellar nerve arises as abranch of the nerve of the lateral oeellus of the corresponding side.In Bombus, where in an immature stage the median oeellus is elon-gated laterally or even slightly constricted to form a lobate oeel-lus, it is likely that at that period the two nerve branches supply-ing it are practically distinct throughout.The question arises whether the occurrence of two median oeellishould be considered as a reversion to some ancestral type, orshould be looked upon as a variation having other significance.The fact that a tendency to a doubling of the ocellus .is apparentin the pupal stage of ttymenoptera but later disappears in theadult might lend support to the former view. However, as, sofar as is known to the writer, no normal examples of a double me-dian ocellus occur in lower insects, it would seem that the case inBombus should be explained in some other way--possibly as merelythe mechanical result due to the double origin of the nerve andthe crowded condition of the organs of the head in bees.In the case of the abnormal doubling of the ocellus in the grass-hopper it would seem to the writer that the explanation probablylies in some unusual influencing factor during its embryologicalperiod.THE SECOND INTERNATIONAL CONGRESS OF ENTOMOLOGY.Since the preliminary notice which appeared in PSYCHE for Feb-ruary, the date of meeting for the congress at Oxford has beenchanged.The meetings will extend from the fifth to the tenth of August,191, and a large and distinguished attendance is expected.Viallanes, I-I. Le Cerveau de la Gupe (Vespa crabro et vulgaris) Ann. Soc. Nat. Zool.1887 7 Set. II, pp. 5-100, 6 pl.Janet, Chas. 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On a Supernumerary Median Ocellus in Melanoplus Femur-Rubrum

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On a Supernumerary Median Ocellus in Melanoplus Femur-Rubrum

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