single ventral embryonic region. The ventral shafts, 

 according to Grube, on the ventral side of the leech embryo 

 play the same role which the dorsal shafts play in the 

 vertebrate embryos, because from them the wall of the body, 

 in particular its muscles, is formed. The ventral shafts are 

 composed of extremely small, closely adjacent other globules. 

 At the posterior end of the embryonic field remain large 

 globules which form part of its molecular (protoplasmic) 

 content; three of these terminal globules usually are present 

 on each side (Figure 36, k) . The internal part of the yolk 

 globule (the divided ovum) constitutes a mass containing 

 little protoplasm. This rich yolk mass is used mainly for 

 building organs which are present in the abdominal cavity, 

 in particular the intestinal canal; above it a layer grows, 

 composed from a molecular mass which takes its origin from 

 the ventral shafts. 



The rudiment of the neural cord appears in the form 

 of two white stripes, joined to the external side by the 

 recently formed embryonic stripes. After their closure on 

 the ventral sides, the halves of the paired rudiment of the 

 nervous system are united. 



In this period the surface of the embryonic body is 

 already covered with epithelium, composed of flat cells of 

 different sizes and forms. At the same time in the body 

 cavity dissepiments are situated, their number gradually 

 increasing. 



In the third part of Grube f s work he included changes 

 occurring after the hatching of Clepsine from the egg 

 membrane. Contrary to Filippi, Grube found very essential 

 differences between the just-hatched leech and the formed 

 worms. In the short, cylindrical little worm hatching from 

 the egg, there are still no posterior sucking discs, no eyes, 

 no blood vessels, and the formation of the dissepiments is 

 also unfinished. As the young larvae are also immediately 

 fixed by the anterior end, Grube assumed the presence of the 

 rudiment of the anterior sucker with longitudinal and circular 

 muscles. Within one day after hatching this sucker is clearly 

 noticeable in the form of a convex ring; after two days 

 this ring elongates, as Grube thought, under the effect of the 

 heaviness of the body of the leech hanging on it. Inside the 

 elongated ring a canal appears representing, according to 



525 



