CHAPTER XIII. 



DISCOPHORA 1 . 



THE eggs of the Discophora, each enclosed in a delicate 

 membrane, are enveloped in a kind of mucous case formed by a 

 secretion of the integument, which hardens into a capsule or 

 cocoon. In each cocoon there are a limited number of eggs 

 surrounded by albumen. The cocoons are attached to water- 

 plants, etc. In Clepsine the embryos leave the cocoon very 

 soon after they get rid of the egg membrane, but in Nephelis 

 they remain within the cocoon for a very much longer period 

 (27 28 days after hatching). The young of Clepsine, after 

 their liberation, attach themselves to the ventral surface of their 

 parent. 



Our knowledge of the development of the Discophora is in a 

 very unsatisfactory state ; but sufficient is known to shew that it 

 has very many points in common with that of the Oligochaeta, 

 and that the Discophora are therefore closely related to the 

 Chaetopoda. In Clepsine there is an epibolic gastrula, and 

 mesoblastic bands like those in Euaxes are also formed. In 

 Nephelis however the segmentation is very abnormal, and the 

 formation of the germinal layers cannot easily be reduced to an 

 invaginate gastrula type, though probably it is modified from 

 such a type. Mesoblastic bands similar to those in the Oligo- 

 chaeta occur in this form also. 



The embryology of Clepsine, which will serve as type for the 

 Leeches without jaws (Rhyncobdellidae), has recently been 

 studied by Whitman (No. 365), and that of Nephelis, which will 



1 The Discophora are divided into the following groups. 



I. Rhyncobdellidse. 

 II. Gnathobdellidse. 

 HI. Branchiobdellidse. 



