REPRODUCTION AND DEVELOPMENT 



111 



the anterior and posterior ends of the cKtellum are greatly con- 

 stricted so that the cocoon is formed in a lemon shape. The inner 

 surface is smoothed by turning the body of the leech about its 



Fig. 62. Erpobdella lineata in process of cocoon formation. 



(a) rotating the body to shape the inner wall of the cocoon; 



(b) withdrawing the body by pulling backwards; (c) the cocoon. 



From Nagao, 1957. 



longitudinal axis and when this is done the whole of the anterior 

 part of the body is made as long and thin as possible by contraction 

 of circular muscles. Into the space left between the body of the 

 leech and the wall of the cocoon is passed an albuminous nutritive 

 fluid and a number of fertilized eggs. The anterior part of the 

 body is then slowly worked backwards out of the cocoon. As the 

 head passes the anterior and posterior apertures of the cocoon 

 these are sealed off by means of a plug produced by the glands of 

 the anterior sucker. At this stage the cocoon is a soft, translucent 

 and colourless bag. The leech now proceeds to flatten it into an 

 elliptical sac of the form shown in Fig. 63 and in a few days it 

 becomes dark brown, hard and almost opaque. The parent takes no 

 further interest. 



In the Piscicolidae, Hirudidae and Haemadipsidae the process 

 of cocoon formation is very similar except that the cocoon is not 

 pressed flat but is allowed to retain its rounded shape. Moreover, 



