EXAMINATION OF CYSTICERCOID STAGES 169 



Asellus aquaticus is the intermediate host of Echinorhynchus angus- 

 tatus, which inhabits the carnivorous fish of these latitudes, and also 

 of E. hceruca of frogs. Gammarus pulex, the water-flea, harbours the 

 intermediate stage of various species, one being E. proteus of fish. 

 The larvae of the may-chafer (Melolontha vulgaris) and of the gold- 

 chafer (Cetonia aurata) are the intermediate hosts of E. gigas. 

 Asellus is an easy subject for experiment, as it may be obtained in 

 large numbers and will live in aquaria. 



The entire complicated developmental change occupies two or 

 three months or even longer, according to temperature. It is not 

 possible to describe here the process by which this change is accom- 

 plished, especially as certain of its details are still in dispute. The 

 student is referred to the literature of the subject, 1 with the study of 

 which he is strongly advised to combine the preparation and examina- 

 tion of sections in series. 



Note : HIRUDINEA (LEECHES). 



Hirudo medicinalis may be procured from any apothecary ; such 

 animals are, however, usually empty, and when in this condition are 

 not suitable subjects for experiment. Leeches should be kept in a 

 glass bowl containing water, and a cloth should be tied over the top. 

 Shortly before examination they should be fed on frogs, which should 

 be introduced into the vessel with the leeches. The wound inflicted 

 by the leech upon the body of the frog should first be examined ; it 

 will be seen to be three-rayed, the semi-circular edges curving inwards. 

 The leeches should be killed in a wine-yellow solution of chromic acid, 

 to which a few drops of glacial acetic acid has been added. They 

 will contract very strongly, and as soon as they have ceased to move 

 they should be stretched out with the fingers. They should be 

 allowed to remain in the fixing fluid for a few minutes longer and 

 then taken out, rinsed in water, and the external appearances should 

 be studied. 



The body is long and narrow with a plane ventral surface, towards 

 which the terminal suckers are directed. The dorsal surface is some- 

 what more arched, and the two aspects differ in colour. The hinder 

 end is recognized by the large disc-like sucker, while at the head 

 end, which is somewhat narrower, is placed the small, slightly pro- 

 jecting anterior sucker. The opening of the intestine is situated 

 upon the dorsal surface in the middle line, just above the large sucker. 

 By opening the oral sucker with a pair of tweezers, three whitish 



1 See Leuckart, Kaiser, Hamann. 



