684 EMILY RAY GREGORY, 



with sand and decayed wood, I carried them back to Chicago in my 

 hand. Unfortunately, I was just then forced to leave Chicago for 

 three months, but the eggs were, through Dr. Wheeler's kindness, 

 kept in the laboratory for me, and the embryos killed from time to 

 time during July and August. On sorting this material carefully, 

 after my return in October, I found few very young stages of Aromo- 

 clielys and no advanced stages of Flatypeltis^ so that many of the Platy- 

 peltis eggs must have come to some sad fate. This material busied 

 me during the winter of 1897 — 98, and in the summer of 1898 I 

 went again to Vawter Park, staying from July 5th until August 11th. 

 For several reasons, mainly because it was a little late and the nest- 

 ing places had already been searched by others, I did not procure 

 many young stages of either kind of turtle, but secured a fine lot of 

 embryos of Platypeltis from 10 mm long up to the hatching time, 

 making with those of the year before quite a complete series of this 

 species. Returning to the University, my time since August Uth 

 1898 has been given to the preparation and study of this material. 

 It would seem that the turtle cannot be very sensitive to adversity 

 even in its embryonic condition. Of twenty-seven series cut before 

 the end of November, none had to be discarded and but two or three 

 show injured tissues, or abnormal conditions. 



During the past summer almost all my material was fixed in 

 chromic acid, P/o» or in sublimate acetic (Kaiser's formula). There 

 was no running water at hand, so I was forced to wash the chromic 

 material as best I could by using large quantities of water and 

 changing it frequently. The sublimate material was washed in 707o 

 alcohol, with iodine added and hardened in 95 7o or absolute alcohol. 

 All the material was preserved in alcohol of 70% or 85 7o- A. few 

 embryos were killed in chrom. os. acetic, a few in nitric, and a number 

 in picric acid. The sections, with few exceptions, were cut 10 f.i thick. 

 For my present purpose I have found iron haematoxylin followed by 

 orange G the most satisfactory stain, although I have also used Dela- 

 pield's haematoxylin, borax carmine and picrocarmine. 



The youngest stage (I) which I have preserved shows the be- 

 ginning of the embryonic shield. Stage II consists of embryos of 

 from 2.8 to 4.5 mm in length, which have from 9 to 15 somites. 

 Stage III contains embryos 6.5—7 mm long with from 11 to many 

 somites. The lens of the eye is invaginated and the head bending. 

 Stage IV has embryos from 6.8 to 8 mm long, and somites are formed 

 to the end of the body. In stage V the limb buds are conspicuous. 



