Abbreviated Larval Period of Rana Catesbeiana in Iowa

It has long been reported that the larval period of Rana catesbeiana in the North lasts for two years (Pope, \u2747, Wright and Wright, \u2749, Smith, \u2750). Examination of tadpoles from such ponds indicates that two age classes are present. The two groups result from the fact that eggs are deposited every year while tadpoles transform only after their second winter. In the light of this information, we were quite surprised to find bullfrog tadpoles apparently of only one age group in Iowa City. 1 In view of this general information, it seems possible that bullfrog tadpoles in this vicinity undergo an abbreviated larval period. Premature metamorphosis of these tadpoles may occur in even more widely distributcd areas since Klimstra (‘47) reports similar observations on Rana catesbeiana from several farm ponds in southern Iowa. In these ponds which were newly· constructed, transforming tadpoles were seen one year after adult bullfrogs first invaded them. Measurements of the tadpoles seemed to fall in one group, ranging in size from 4.1 - 5.9 inches. Unfortunately the number of tadpoles which were measured was not reported. Since all these observations of abbreviated metamorphosis seem to be of such general nature, we decided to follow closely the life history of bullfrog tadpoles in two large ponds on the Rohner farm about five miles south of Iowa City

The Mesencephalic Nucleus of the Trigeminal Nerve in Young Snapping Turtles

The mesencephalic root of the trigeminal nerve is a constant feature of all gnathostomes. The cells of origin of these root fibers lie mainly within the midbrain. Peripherally the fibers are distributed to the musculature of the jaws, and they constitute the proprioceptive apparatus of that musculature (Corbin and Harrison, \u2740). Although the large mesencephalic V nucleus cells have been recognized for about 90 years (Meynert, \u2767), adequate descriptions of their size, numbers and distribution are still not great. Perhaps the most comprehensive study is that of Weinberg (\u2728) on fifteen different species in five of the classes of vertebrates. Among these was a turtle, Chrysemys marginata. The present study was undertaken to compare the mesencephalic V nucleus cells in the snapping turtle with the cells previously described in Chrysemys

The Influence of Growth Rate Upon Brain development in Rana Pipiens Tadpoles.

In the course of studies on the development of the optic tectum in the frog (Kollros, \u2753), considerable variation in the cell populations of the outermost tectal layers was noted, with some involvement of the deeper layers as well. The greatest differences appeared toward the end of metamorphosis, with cell counts in some animals being 30 to 40 per cent less than those in others. The animals with low counts were generally smaller than those with the high counts, and frequently they grew more slowly. In order to study the variations in tectal development which might be associated with variations in growth rate, the growth of tadpoles was inhibited through partial starvation and by crowding (see Rugh, \u2734), and the cell counts of the tecta of these animals were compared with those of well fed, uncrowded control animals