- 5 .— 



It is not possible to distinguish any further details 

 superficially, the material having, unfortunately, been 

 kept too long in alcohol. 



Sections through the egg at this stage show that the 

 blastoderm already consists of the three germinal layers. 



The ectoderm consists of a continuous epithelium or 

 layer of cells covering the surface of the egg. The walls 

 of these cells are distinctly visible. The cells them- 

 selves are rounded, their nuclei fairly large and somewhat 

 oval; they measure "01 mm. in length by '007 mm. in breadth. 

 The chromatin is not evenly distributed, but forming a 

 number of small particles, gives the nuclei a spotted 

 appearance. This layer is sometimes as much as three 

 cells deep. " 



The mesoderm lies directly under the ectoderm. The 

 cells forming it are disconnected; whether they form a 

 continuous layer in life or not I am not able to decide, 

 as the cells may have shrunk in alcohol. Between the 

 cells of the mesoderm yolk-particles are often to be seen, 

 which makes it probable that the mesoderm never con- 

 sisted of a continuous layer. The nuclei of the mesoderm 

 cells are larger than those of the ectoderm, and also 

 rounder; they measure .014 mm. in diameter. 



The cells of the mesoderm seem to be engaged in 

 rapid reproduction, karyokinetic phenomena being very 

 frequent, and the centrisomata very often visible. 



The entoderm consists of single cells, lying deeply 

 embedded 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 blastoderm. 

 Where the yolk penetrates the mesoderm, and in all 



