1922] Notes on the Texas Horned Lizard 135 



gravid females present a ' ' stuffed ' ' appearance. Within their leathery 

 shells the eggs float in a sero-albuminous liquid and so easily that the 

 blastoderms, after the shells are formed, invariably float upward, as 

 in the laid eggs of the fowl, directed toward the back of the mother 

 on which the rays cf the sun fall. During the first few hours after 

 the ova are received by the ostia, and before the shells are formed, the 

 germinal discs are directed cephalad, a circumstance which seems to 

 spell suction by the ostium, the discs of the ovarian eggs being invari- 

 ably directed dorsad and away from the point of dehiscence of the 

 follicles. |As the body of the mother is much flattened the eggs lie 

 usually in but one layer and never far from the dorsal surface. The 

 utility of this form of body as an incubator is thus evident. 



the role of wandering mesenchyme cells 

 As shown by Jarvis ('08) the germ-cells of Phrynosoma arise out- 

 side the embryo upon the yolk-sac and migrate along the yolk-stalk to 

 the germinal ridges. Stockard ('15), more recently, has made an 

 elaborate study of the role of wandering mesenchyme, showing its 

 importance in the development of Fundulus, 



It was my privilege, in the examination of embryos of many stages 

 in Phrynosoma, under the binocular, both to observe the development 

 of the circulation and its course in the embryonic vessels, and also to 

 witness the importance of extra-embryonic amoeboid cells (wandering 

 mesenchyme?) which appear in large numbers in the yolk beneath 

 the embryo in this lizard. 



Very soon after embryonic development begins these amoeboid cells 

 may be found, first in a thin layer and later in a disc-shaped mass, in 

 the thin yolk under the embryo. The mass referred to is of a yellow- 

 ish-green color. The individual cells are hyaline or faintly granular 

 and show active amoeboid movement. That these cells are important 

 in many ways in histogenesis seems certain. They warrant a thorough 

 study in this or a related reptile in the spirit of Stockard 's work on 

 Fundulus. 



EGG-LAYING AND INCUBATION IN THE NESTS 



The nest-building and egg-lajdng habits of this species have been 

 studied by Strecker ( '08 ) in Texas and my observations are in essen- 

 tial agreement with his. The female digs out a slanting burrow 

 several inches in depth on a sloping hillside and prefers a site just 



