166 ZOOLOG Y. 



means of their spines, through the intestine into the body- 

 cavity of the larva, where they become encysted, and the latter- 

 being in the beetle state devoured by the pig, finish their de- 

 velopment in the intestines of the latter animal. (Schneider.) 

 The embryos of this species also occur in the land-snails, and 

 those of E. daviceps have been found in fresh-water snails 

 (Limncea). Young Echinorhynchi occurring in thecopepod 

 crustacean, Cyclops, become mature in a fish (Gadus lota}. 

 Leuckart has also found that a sexless form living in a fresh- 

 water crustacean, Gammarus pidcx, becomes developed to 

 sexual maturity in the perch, which feeds on the crustacean. 

 They attain the mature form, though the eggs are not ripe, 

 in eight or ten weeks after the eggs from which they hatch are 

 laid, and look like round or oval yellowish balls from one to 

 one and a half millimetres in length. The males mature in 

 about a week after the females. 



The primary host of EcMnorliynclnis anyustatus is the 

 fresh-Avater sow-bug (Asellus}. After the eggs find their 

 way into the intestines of the Asellus, the embryos, on hatch- 

 ing, pass through the walls of the hinder part of the chyle- 

 stomach of the Asellus into the body-cavity, by means of 

 the embryonal, deciduous neck apparatus ; and, as in E. 

 profeus, the embryos lie between the chitinous walls of the 

 intestine and the muscular layer. The embryos are round- 

 ed, more or less spindle-shaped, with a so-called rudimentary 

 digestive cavity indicated by a central circle of cells, the 

 cells of the body- walls being situated in a parenchymatous or 

 protoplasmic mass (plasmodium), being thus comparable to 

 the blastoderm of some insects. The embryo is 0.09-0.1 

 millimetres long. The form of the body now becomes irreg- 

 ularly oval or cylindrical, being quite protean in shape, with 

 often a projection on one side of the end of the body. The 

 Echinorhynchus form then begins to appear, the metamor- 

 phosis being very marked. The first step is the moulting of 

 the embryo or larva, which loses its spines. After a few 

 weeks the Echinorhynchus form is attained, the body being 

 elongated, and with the reproductive organs developed, but 

 with no hook-apparatus. It is now 7 to 8 millimetres in 

 length, and almost as long as its host, the Asellus ; the males 



