Seasonal Variation in Birds

Wild birds show cyclical alternation between breeding seasons and seasons of sexual inactivity. During the latter the sex glands are at rest and are very small. With the approach of the breeding season they start to grow rapidly, -- increasing in volume up to one thousand times. Accompanying this growth of the gonads many secondary sex characters also show a characteristic development. This is true in first respect for the sperm- and oviducts, but also external secondary sex characters often show striking changes. The bill color of the sparrow is light brown during the resting period and becomes blue black in the breeding season. In some birds, as the Rose-breasted Grosbeak, a remarkable change also takes place in the plumage. Experiments have been performed and will be presented to show the external and hormonal factors that control these seasonal changes

The Cherokee Frog, Rana sylvatica cherokiana nom. nov., of the Appalachian Mountain Region

Locality: Murphy, North Carolina, elevation 462 m (1540 ft.) (Appalachian Mountains), January 1953. Live Size: Female, nose to anus 82 mm, toe to toe (4th) 270 mm. Male, nose to anus 67 mm, toe to toe (4th) 248 mm. Shape: Typical body shape of brown frogs, with straight and rather pointed rostral head. Dorsolateral folds, from the dorsal circumference of the ear to the caudal fusion above the anus. Diameter of tympanic membrane 5.5 mm in the female, 5.0 mm in the male

THE PRESENT STATUS OF THE GERM-CELL PROBLEM IN VERTEBRATES

(i) Morphological studies relating to the origin and differentiation of the definitive germ cells in vertebrates have, as indicated, resulted in conflicting views. In many instances two or more competent investigators who have studied the same form have reached different conclusions. (2) Some contend that the germ cells are set aside from the soma during the early stages of embryonic development, and that these alone serve as the progenitors of the functional sex cells. (3) Others recognize an early differentiation of sex cells but hold that these are supplemented by others produced from the somatic epithelium of the gonad in late embryonic or post-embryonic stages. (4) Another group recognizes the early differentiated cells as germ cells but contend that these all degenerate and that the definitive ones are formed from the germinal epithelium. These degenerating germ cells are believed by certain authors to be a phylogenetic recapitulation of the condition in lower forms. (5) Finally, yet another group contends that the so-called primordial germ cells are not germ cells at all but are enlarged cells in some stage of mitosis or in some specific metabolic phase. This group believes that all germ cells are derived from the somatic cells of the germinal epithelium. (6) Experimental work supports the view that the primordial germ cells, which are recognized early, are the progenitors of the definitive sex cells. When these primordial germ cells are prevented from reaching the site of the developing gonad the individual fails to develop sex cells, although a sterile gonad and its associated structures may develop. (7) I suggest that the observed proliferation of germ cells from the germinal epithelium, reported by numerous investigators, can be interpreted in another way by a thorough study of the enlarged germ cells in relation to the epithelium. It seems probable that the cells of the epithelium, which form functional sex elements, are not and never were a part of the mesothelial covering, but are cells which were segregated early, and are merely stored in the epithelium.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74677/1/j.1469-185X.1945.tb00313.x.pd

Der Hermaphrodismus der Frösche und seine Bedeutung für das Geschlechtsproblem und die Lehre von der inneren Sekretion der Keimdrüsen

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