600 h. FT. GOUGH. 



embedfled in the yolk. Generally only the nuclei of these 

 cells are to be seen. The nuclei are of about the same size 

 as those forming the ectoderm, measuring "01 mm. by "012 mm. 

 Their shape is sometimes convex-concave. Their chromatin 

 is very evenly distributed, but still presents a slightly 

 granular appearance. 



These three germ layers correspond in appearance and 

 position very closely to the same three of spiders, as 

 described in the handbook of Korschelt and Heider (26). 



The yolk only differs from the description given in the 

 first stage in the parts nearest to the bhistoderm. Where 

 the yolk penetrates the mesoderm, and in all parts adjacent 

 to the same, the yolk spherules have become very small 

 indeed; which would lead one to think that the mesoderm 

 is causing the yolk to break up. 



The outer membrane shows no difference from that 

 described in Stage I. The inner has, however, changed 

 since the first stage, having risen above the surface of the 

 egg in the region of the blastoderm, leaving a free space be- 

 tween itself and the ectoderm. 



Stage III. 



The third stage at my disposal is considerably more 

 advanced than the last. The reversion of the embryo has 

 already taken place, and the extremities have begun to grow. 

 I have only found one egg at this stage ; it comes from the 

 same batch as the eggs described under Stage I and Stage 

 IV. Its growth had evidently been stopped by the pressure 

 of the surrounding eggs, which also caused the embryo to 

 develop in two disconnected halves, only held together 

 by the yolk. The embryo also showed several other signs 

 of not having developed normally. 



My sections through this egg are, unfortunately, not all 

 that I could wish, but still they are good enough to make 

 out several details. For this reason I shall only attempt to 

 describe a few of the organs. 



