144 



THE 



PART I 



brings about the contraction of the membrane for the 

 discharge of the eggs. 



The nuclei of the nutritive cells grow to an enor- 

 mous size, and clearly play the chief part in absorbing 

 material for the formation of the yolk. When the 

 egg is ripe, these nuclei come to the surface and 

 gradually disappear. 



FIG. 33. Eggs at different stages. In stage i the definitive egg nucleus is already 

 differentiated from the nuclei of the three nutritive cells; the latter are seen to 

 grow very large and coarse, and then in 5 to move to the side where they 

 eventually disappear. In 5 the yolk discs fill the whole egg, making the nucleus 

 difficult to see. At 6 an egg has been discharged ; the follicular membrane has 

 shrunk, its contents being probably dislodged epithelial cells, f, testes as 

 occasionally found (e.g. in A. cancriformis)\ n, nuclei of follicular epithelium. 



The egg, in its passage down the genital tube and 

 along the longitudinal oviduct, gets covered with a 

 slimy substance yielded by the deep club-shaped 

 epithelial cells. This substance hardens into a shell 

 for the protection of the egg, a shell which, as Von 

 Siebold remarks, looks as if made of hardened foam. 

 The eggs pass out between the loth and nth pairs of 



