134 Journal of the jMitchell Society [31 arch 



mone, — where, and under what circumstances secreted we are now un- 

 able to state. 



GENERAL FEATURES OF EMBRYONIC DEVELOPMENT 



In the correlation of stages in lacertilian embryology we are greatly 

 aided by the Normentafel of Peter ('04), on Lacerta agilis, in the 

 Keibel series. But while in general parallel, the ontogenetic develop- 

 ment of Phrynosoma is more extended and, in the later or foetal stages, 

 much more specialized than that of Lacerta. These later differences 

 depend but little on any diversities inherent in the two families rep- 

 resented but rather on the emergence of highly specialized generic 

 characters, such as the shortened and broadened body, horns, and 

 rosettes of scales, the appearance of which overpowers the more fun- 

 damental iguanid characters. 



We are here, however, concerned with the oecology of this reptile 

 in relation to reproduction. As one species of Phrynosoma is vivip- 

 arous and others oviparous an interesting problem exists in the re- 

 lation of the period of egg-laying to the stage of development attained 

 at that time. In the common fowl the egg is laid while the embryo 

 is undergoing later segmentation. In lizards the eggs are usually re- 

 tained much longer, the coelomic cavity of the mother serving as an 

 incubation chamber for the eggs lying within the convoluted oviducts. 

 The precise stage at which laying takes place seems to be a matter of 

 no consequence, lending itself easily to the development of the ovo- 

 viviparous habit of P. douglassi, in which species the eggs hatch while 

 or immediately after being laid. There is reason, also, for the belief 

 that captivity extends the pre-laying period, in reptiles, by several 

 stages. 



In P. cornutum 1 found little constancy in this matter, some laid 

 eggs being as early as Peter 's stage 22, others as late as stage 28 or 30. 

 Lizards being poikilothermal much must depend on the temperature 

 of soil and air as well as on the time necessary for the gravid female 

 to find a situation suitable for a nest. Specialized generic and specific 

 characters also here tend to prolong the ontogenetic period within the 

 egg and to extend it beyond the range of Peter's series, his final stage 

 (36) being comparable to Phrynosoma embryos several days and 

 stages removed from the laying period. 



As above stated the coelomic cavity serves, during the breeding 

 season, as a brood-pouch, the 30 or 35 eggs packing it so full that 



