72 JOURNAL OF THE 



temperature below the normal temperature of incuba- 

 tion, in order to lessen the rapidity of development. A 

 certain percentag'c of abnormalities was to have been 

 expected from the use of the temperature below the 

 normal, and I have satisfied myself that at 35° various 

 kinds of abnormalities do occur. Out of a considerable 

 number of young- blastoderms, incubated at 35°, while 

 the majority showed no trace of the sickle, in a few 

 cases the primitive streak exhibited abnormalities sugf- 

 g-esting- more or less strongfly the sickle. Surface 

 views of two of these blastoderms are g-iven in Fig's. 1 

 and 2. In the primitive streak of Fig\ 2, I could not 

 make out the primitive gfroove, but the g-roove was very 

 evident in the sickle at the posterior end of the streak. 

 (Kupffer and Benecke'^ g-ive a wood-cut iig-ure of a chick 

 blastoderm, quite like m}^ fig-ure 2, except that the 

 primitive gfroove is shown. While they incline to the 

 belief that the sickle in such a blastoderm is of morpho- 

 log-ical importance, they admit that it was only rarely 

 that such blastoderms were found.) In the blastoderm 

 shown in Fig*. 1, the g-roove was conspicuous, both in 

 the streak and in the transverse outgfrow^ths of the 

 streak. This blastoderm was sectioned long'itudinally. 

 A median section througdi the streak is shown in Fig\ 

 3. The transverse g-roove is deep; the hypoblast is 

 differentiated as a distinct layer; the epiblast and meso- 

 blast are mdisting-uishably fused. In Fig-. 4 is repre- 

 sented a section l3^ing- in the plane x-y of Fig- 1. In 

 this reg-ion the transverse g-roove is as deep as in the 

 median section, but the three layers are separate. 



Mv feiilure to find the sickle in blastoderms where, 

 according- to KoUer it should be present, and the obser- 



5. Die ersten Entwicklung-s vorg-ang-e am Ei der Reptilien. Koiiig-s- 

 berg. 1878. p. 11. 



