166 ZOOLOGY. 



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. claviceps have been found in fresh-water snails 

 {LimncBo). Yonng Bchinorhynchi 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 pulex, becomes developed ta 

 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 ta 

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

 about a week after the females. 



The primary host of Ecldnorhynchus ancjustatus is the 

 fresh-water 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. 

 proteu/t, the embryos lie between the chitinous walls of the- 

 intestine aud 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 

 v/eeks the Echinorhynchus form is attained, the body being 

 elongated, and with the reproductive organs developed, but 

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

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



