CH. I] EARTHWORMS AND LEECHES 31 



like cocoon. The eggs hatched in 30 days producing 

 young inch long, which speedily fastened on to tadpoles. 

 The adults died a few days after laying the eggs. 



The Medicinal Leech and Horseleech deposit their eggs 

 in capsules which are attached to submerged plants and 

 similarly situated bodies, or are buried in the mud or in 

 holes in the banks. The cocoon of the latter species 1 is 

 oval, about half an inch long, of a greenish-brown colour. 

 It consists of an outer, loose, spongy case surrounding the 

 central more compact envelope of the inner chamber, within 

 which is a dense semi-transparent gelatinous substance in 

 which are embedded some ten pear-shaped eggs. 



The cocoons are formed, as in earthworms, in the 

 shape of rings open at each end and completely sur- 

 rounding the segments by which they are secreted: the 

 leech withdraws the anterior part of the body, sliding 

 backwards out of the cocoon as out of a collar. It is said 

 that the cocoon is fastened to some foreign object by 

 means of the mouth. 



A small but common leech, Nephelis vulgaris*, which 

 occurs in most ponds and sluggish streams, deposits brown 

 capsules of eggs on the underside of the leaves of water 

 plants among the eggs of fresh-water snails. The eggs are 

 laid in June and hatch in about six weeks. This leech 

 sucks the blood of snails, but small Crustaceans and even 

 Rotifers are found within its digestive cavity. The habits 

 of Nephelis tesselata* are somewhat different, the young to 

 the number of 200 or more remaining attached to the 



1 Bowerbank, Ann. Mag. Nat. Hist. 1845. 



2 Brightwell, loc. cit. 



