1922] Notes on the Texas Horned Lizard 133 



to date, been published whereby the early segmentation stages might be 

 found except by accident. Thus the series of embryos of Lacerta 

 agilis, described and figured by Peter in his Normentafel, required 

 six summers to complete. 



In my work on Phrynosoma, after much practice in external palpa- 

 tion as well as in dissection of apparently gravid females, it became 

 possible, in many cases, by palpation only, to distinguish between 

 ovarian eggs and those which had passed into the ducts. The mass 

 of large ovarian eggs is always smaller in area and more dense, that 

 of the oviducal eggs more diffuse and softer. I found, however, that 

 the two conditions, unfortunately, merge at just the critical time, i. e., 

 with approaching ovulation the ovarian eggs become larger, softer, 

 and less well-defined, which condition merges with that of the early 

 oviducal ova. 



After much vexation caused by the sacrificing of females in which 

 ovulation had not yet occurred and others in which the embryos were 

 too far advanced, and after seeking, in vain, aid through use of the 

 flouroscope, I discovered that exploratory operations do the creatures 

 practically no harm and hold out much promise for future success 

 in this field of embryology. The animals recover and may be opened 

 and sewed up again several times. If seeking segmentation stages one 

 may thus await ovulation. If the eggs have passed into the ducts one 

 of the latter may be dissected loose, ligatured at base and removed 

 with its eggs, the other being left to develop further. 



It is interesting to observe that, whereas we are unable to explain 

 the cause of ovulation the dehiscence of about thirty-two large folli- 

 cles takes place, so far as we know, almost simultaneously. A change 

 so momentous requires an adequate cause. Up to the time of ovulation 

 the ova are held firmly in their follicles. (There are no visible cica- 

 trices in Phrynosoma.) Then, suddenly, the ova are all shelled out and 

 rapidly engulfed by the ostia. 



The time-relation between copulation and ovulation has been much 

 studied by vertebrate embryologists with two main results. In some 

 vertebrates, as in the rabbit, a definite interval (nine or ten hours) 

 has been found to exist. In others, as the lizards, there is no known 

 time-relation. 



Although we have no evidence to that effect it is our belief that 

 ovulation in Phrynosoma must depend upon the liberation of a hor- 



