132 Journal of the Mitchell Society [March 



eggs are, in each ovary, divided into two groiijDs, one placed laterally, 

 the other mesially in relation to the mesovarium. 



Still further dorsad, or lying among, this second group of eggs, 

 are ova of a third order as to size, as yet clear and apparently alecithal. 



The condition here observed obtains, doubtless, in many other 

 vertebrates which show a strictly annual periodicity in their egg-lay- 

 ing. So far as we know ovulation in this species takes place rather 

 suddenly, the thirty-two-odd ripe follicles undergoing dehiscence 

 within a few hours, leaving the empty follicles to be resorbed and al- 

 lowing the next order, or half -grown eggs, to develop to full size during 

 the year following. Meantime the third, or smallest group, from 

 among the remaining oogonia, acquires yolk in its turn. Thus, in 

 Phrynosoma, we observe, in correlation with an annual periodicity in 

 egg-group ovulation, an annual initiation of yolk-secretion by the 

 follicles of groups of undeveloped oocytes against the layings of future 

 years. According to the terms of this hypothesis the secretion of the 

 yolk of any egg requires two years. 



the oviducts 

 In birds the ova are treated seriatim by the oviduct in the laying 

 down upon them of the albumen, shell-membranes, and shell. The ovi- 

 duct of the Homed Lizard, on the contrary, is adapted to the simul- 

 taneous investment with albumen and shell of sixteen or more eggs 

 carried tandem in its coils. A seriation in this process along the two 

 egg-strings is practically absent, the albumen, which is serous in con- 

 sistency and very small in amount, as well as the shell, being evidently 

 secreted by the same region of the duct in situ rather than by suc- 

 cessive regions traversed by the egg in its course. 



OVULATION AND EARLY DEVELOPMENT 



From a number of observations it is evident that, in Phry^iosoma, 

 maturation occurs immediately prior to ovulation and that fertiliza- 

 tion ensues immediately upon the entrance of the egg into the ostium. 

 In studies of lacertilian embryology the securing of segmentation 

 stages is, however, very difficult. The writer was able to confirm the 

 statement of Peter ( '04) that there is no relation between the time 

 of copulation and that of ovulation. Further, the same female may 

 copulate more than once. 



Having no way to tell the exact hour of ovulation no method has, 



