346 



THE ANIMAL PARASITES OF MAN 





m 



dorso-ventral direction ; the muscular system is subject to a particular 

 expansion in the clinging organs and at the commencement of the intestine. 

 On the whole, the alimentary canal represents a tube running straight from 

 the mouth to the anus, which possesses a number of 

 blind sac-like protuberances at the sides varying according 

 to the species. The most anterior section, the pharynx, 

 in the leeches with maxillae, carries three chitinous, semi- 

 circular plates furnished with teeth the jaws which 

 serve to tear up the epidermis in order to open the 

 blood-vessels ; in the . leeches with rostra a long pro- 

 tractile proboscis rises from the base of the elongated 

 pharynx. Numerous salivary glands, the secretion from 

 which possesses toxic properties, discharge into the 

 pharynx. The oesophagus, which follows the pharynx, 

 and to the exterior of which numerous radiary muscles 

 are fixed, is a suctorial organ in its entire structure. 

 The nutriment in the larger species consists of the 

 blood of vertebrate animals, in smaller species and 

 in the young stages the food consists of small inver- 

 tebrate animals. 



The NERVOUS SYSTEM exhibits the typical structure 

 of other segmented worms ; the sensory organs consist 

 of the above-mentioned goblet-shaped cutaneous sensory 

 organs, of the organs of taste, and of eyes ; the latter 

 frequently being present in large numbers. 



The EXCRETORY or segmental organs exhibit many 

 peculiarities, which cannot, however, be detailed here. 

 They commence with funnels in the lacunes of the body 

 cavity, and usually discharge on the ventral surface. 



Almost all the hirudinea are hermaphrodite and 

 copulate reciprocally. The two ovaries are very small, 

 and the oviducts that proceed from them soon unite 

 into a common duct, which then goes over into the 

 uterus and discharges through the short vagina in the 

 median line of the ventral surface behind the male 

 organs into the so-called clitellar region. The male 

 sexual apparatus consists of symmetrically - arranged 

 testicles, varying in number according to the species, 

 the short vasa efferentia of which, one by one, run into 

 the vas deferens, passing towards the front on each side. 

 In front, at about the level, or a little in front of, the 

 female genitalia, the two vessels pass into a convoluted 

 mass of tubes to the so-called epididymis, and then 

 discharge into the single protractile penis (fig. 226). 



All leeches deposit so-called COCOONS. These are 

 small barrel-shaped, or pouch-like bodies, which are 

 surrounded by a thicker shell, and contain a number 



of eggs in a large mass of albumen ; the albumen originates from glands 

 of the generative organs, the shell-substance from cutaneous glands of the 

 clitellar region. 



FIG. 226. The 

 internal organs of 

 the leech. The 

 creature has been 

 opened from the 

 dorsal surface, and 

 part of the intestine 

 has been removed. 

 The testicles, with 

 vas deferens, may 

 be seen between 

 the blind ducts of 

 the intestine ; be- 

 yond these on either 

 side the segmental 

 organs. The female 

 genital organs are 

 in front of the most 

 anterior pair of tes- 

 ticles. (After Ken- 

 nel.) 



