MOUNT DESERT REGION 9 



them at once, and if the water did not circulate freely enough, 

 they died from the rise in temperature. At this period we 

 were going through abnormally hot weather, and the room 

 temperature in the laboratory was high. 



The degree of development and length of the larvae at their 

 disappearance were somewhat less than the last which Marie 

 Lebour ('25) was able to raise from the egg. It is evident 

 that there is a critical stage in the development of the larvae 

 about six or eight days after hatching when they are 6 or 

 7 mm. in length; something is required at this time which 

 ordinary aquaria conditions cannot supply. 



The history of the development of the embryo and larvae, 

 so far as can be seen by microscopic study of living material, 

 is given by the figures (figs. 2 to 22). Little comment is neces- 

 sary, except to call attention to the most important features 

 of the embryo at each day of development and to give the 

 length, measurements, and temperatures. The figures were 

 drawn by Mr. Simon Cohen, medical student at the University 

 of Kansas and artist of the Survey. 



DESCRIPTION OF EMBEYOS AND LARVAE 



Ju7ie 39th, 4 p.m. Embryos immediately after capture. 



Embryos of younger veil (figs. 1 and 2), probably fertilized eight 

 to twelve hours previously : embryos show blastoderm at one pole of 

 Q^^ with germ ring well formed ; anlage of body visible as a thickened 

 area of the blastoderm extending inward from the germ ring ; single 

 oil globule. Embryos of older veil showed body well outlined and 

 scattered pigment ; slightly more advanced than embryo shown in 

 figure 3. 



June 30th, first day after capture (fig. 3, from younger veil). Tem- 

 perature, 10.30 A.M., 14.7° to 15.0°C.; 3.30 p.m., 14.0° to 15.0°C. 



Anterior part of body well outlined ; blastoderm not quite inclosing 

 yolk; small unexpanded pigment spots along sides of neural cord, 

 also lateral to somites and along edge of blastoderm ; sparsely scattered 

 over rest of blastoderm. 



A later embryo of the same day from the older veil (fig. 4) shows 

 the posterior end of the body beginning to project over the surface 

 of the yolk sac ; blastoderm now completely surrounding the yolk ; 

 pigment on the ventral side of the body; enlargement of the optic 

 vesicle. The heart is first visible at about this stage. 



