26 THÉEL, HERMAPHRODISM IN HOLOTHURIDS. 



the space occupied by the clear calotte which now begins to 

 disappear (Pl. I, fig. 12). The micropyle has acquired the 

 shape of a cone with double contures and its top is j oined to 

 the follicular membrane. It always contains an irregularly- 

 formed peculiar body, which appears well defined and almost 

 black after being stained with iron-hsematoxyline. The future 

 fäte of this body may be discussed further on. 



By degrees, during the progress of the ripening process, 

 the micropyle-cone penetrates the follicular membrane, thus . 

 bringing about a communication between the contents of the 

 ovum and the lumen of the genital tubes. According to Ha- 

 MANN, the conical protrusion of the egg is to be considered 

 as a simple string formed of egg-plasm, finishing in a rounded 

 nucleus-like figure which hängs freely down into the cavity 

 of the genital tubes. However, a careful investigation shows 

 US that it has a rather complicated structure, which may be 

 better understood from the figures given on plate II, 15, 16. 

 In sections treated with iron-hsematoxyline, the deutoplasm of 

 the ovum presents a thin exteriör coat surrounding the in- 

 teriör main-portion, the two constituent parts being well di- 

 stinguishable one from the other; the inner part has, viz, a 

 much coarser mesh-structure, and at the place of between 

 them there is a dark line of demarcation increasing in clear- 

 ness towards the micropyle-cone. 



The outer deutoplasma-coat also reaches its greatest thick- 

 ness at the cone where it forms a circular enlargement round 

 its base. Decreasing again in thickness towards the top of the 

 cone, it forms its envelope and confines a string-shaped pro- 

 longation of the inner coarsely-meshed deutoplasm which even 

 reaches or possibly penetrates the follicular membrane. More- 

 over, in vertical sections through the ovum and the micro- 

 pyle, another structural arrangement is met with. Inside 

 the base or the micropyle-cone, the dark line of demarcation 

 between the two substances emits inwards the coarser deuto- 

 plasm an annular valve pierced in the centrum (fig. 15 v.). 



As mentioned above, Hamann found in Holothuria tubu- 

 losa that a rounded nucleus-like corpuscle was attached to 

 the top of the micropyle and hung freely down into the cavity 

 of the genital tube. In somewhat more adwanced eggs of 

 Mesothuria intestinalis I regularly observed the same myste- 

 rious corpuscle covering the end of the cone like a cap and 



