628 THE ANIMAL KINGDOM. 



the body. Similar folds are found in Lophobdella from the mouth of the 

 Crocodile, &c. Acanthobdella has setae. 



A delicate elastic cuticle, which is moulted and renewed at intervals, 

 covers the body. It is pierced by the orifices of the cutaneous glands, 

 nephridia, &c. The epidermis consists of a single layer of cells, between 

 which there penetrate in all Gnathobdellidae and some Rhynchobdellidae pro- 

 cesses of pigmented connective tissue cells together with blood capillaries. 

 There are numerous integumental unicellular glands of various kinds ; 

 mucous glands which either retain their position in the epidermis, or when 

 large intrude into the dermis ; prostomial glands in Gnathobdellidae, open- 

 ing round the buccal cavity ; salivary glands opening into the pharynx ; 

 and clitellar glands opening on the clitellar somites ; all deeply placed in 

 the dermis and provided with long ductules. The body-walls are composed 

 of an external circular and an internal longitudinal layer of muscles, with 

 an interposed diagonal layer in some instances. These layers are imbedded 

 in a plentiful connective tissue, which forms also a superficial sub-epidermic 

 coat, and consists of a variably developed jelly-like matrix containing cells 

 of various kinds, among them branched connective tissue and pigment cells 

 (see p. 215). Dorso-ventral and radial muscle bundles take the place of 

 the septa of Chaetopoda. 



The nervous system consists of a paired supra-oesophageal ganglion, 

 connected by a very narrow oesophageal commissural ring with the first 

 ganglion of the ventral chain, which consists in most Leeches of twenty- 

 three ganglia, united by longitudinal commissures. The first or sub- 

 oesophageal and the terminal ganglion are formed by the fusion of several 

 embryonic ganglia (p. 219-20). The ganglionic cells have a tendency to 

 form projecting masses on the surface of the ganglia. In Hirudo there are 

 three minute ganglia connected one with each of the three jaws. A sym- 

 pathetic nerve is in relation with the stomach. A variable number of eyes 

 are present on the anterior cephalic annuli and of Piscicola on the posterior 

 sucker. They are entirely absent in some terrestrial forms (Typlobdella^ 

 Cylicobdella, Macrobdelld). Eye-like organs, but devoid of pigment and 

 known as * segmental papillae/ are found on the first annulus of each somite, 

 and sometimes on the posterior sucker in Gnathobdellidae. They occur in 

 Clepsine, and it is possible that they exist also in other Rhynchobdellidae. 

 Sense organs or goblet-shaped bodies, with a structure closely resembling 

 eyes, are scattered in large numbers over the cephalic anrtuli of some 

 Leeches, and on the lips \ 



1 According to Whitman (Leeches of Japan, Q. J. M. xxvi. pp. 396-410), the goblet organs of 

 the lip consist of a clump of elongated hypodennis cells, and of a nerve distributed to the base of the 

 clump in which there are what appear to be ganglion cells. Clear, nucleated, and vacuolated cells 

 are found scattered along the nerves going to these organs. The segmental organs and the scattered 

 sense-bulbs of the head, on the contrary, have a number of vacuolated cells grouped round the clump 



