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 Ciepsine, 

 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 Oligochseta, and that 

 the Discophora are therefore closely related to the Chsetopoda. In 

 Clepsine there is an epibolic gastrula, and mesoblastic bands like 

 those in Euaxes are also formed. In Nephelis however the segmenta- 

 tion is very abnormal, and the formation of the germinal layers can- 

 not easily be reduced to an invaginate gastrula type, though probably 

 it is modified from such a type. Mesoblastic bands similar to those 

 in the Oligochseta occur in this form also. 



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

 Leeches without jaws (Rhyncobdellidre), has recently been studied 

 by Whitman (No. 365), and that of Nephelis, which will serve as type 

 for the Leeches with jaws (Gnathobdellida?), has been studied, by 

 Biitschli (No. 359). The early history of both types is imperfectly 

 known 2 . 



1 The Discophora are divided into the following groups. 



I. Rhyncobdellidse. 



n. Gnathobdellidae. 



in. Branchiobdellidse. 



J Hoffmann's account (No. 36) is so different from that of other observers that 

 I have heeu unable to make any use of it. 



