REPRODUCTION AND- DEVELOPMENT 



113 



the wall is usually differentiated into an outer ornamented or 

 spongy layer and an inner smooth layer (Fig. 65). In the case of 

 the Hirudidae and Haemadipsidae it is thought that one function 

 of the spongy layer is to reduce water loss, for members of these 



mm 



v^i^' 





^' 





'^^Hf,^ 







Fig. 65. Cocoons of Cystobranchus. 1, complete; 2, with 

 spongy layer removed from upper surface. From Hoffmann, 



1955. 



families lay their cocoons on land. Zick (1933) analysed the wall 

 of the cocoon of Hirudo and found that it was a scleroprotein 

 closely related to fibroin, a constituent of insect silk. He proposed 

 for it the name hirudoin. 



The Glossiphoniidae are interesting for the degree of parental 

 care which they exhibit. They produce a very thin-walled cocoon 

 and immediately after deposition they place their bodies over it 

 and assume a protective role. Most glossiphoniids produce the 

 cocoon in the same manner as other leeches, secreting it as a girdle 

 round the body and fastening it to the substratum before backing 

 out of it, but in those species mentioned earlier where the clitellar 

 glands are confined to an area round the genital pores the cocoon 

 forms like a bubble over the genital pores and the eggs are dis- 

 charged into it. The process has recently been described and 

 illustrated for the Japanese leech Glossiphonia lata by Nagao (1958) 

 (Fig. 66). 



At an early stage in development, while still enclosed within the 

 egg membrane, the young glossiphoniid leeches develop an 

 embryonic attachment organ. It takes the form of a knob of 



