124 ZOOLOGY. 
means of their spines, through the intestine into the body- 
eavity 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 Z. claviceps have been found in fresh-water snails 
(Limnea). Young Echinorhynchi occurring in the copepod 
crustacean, Cyclops, become mature in a fish (Gadus ota). 
Leuckart has also found that a sexless form living ina fresh- 
water crustacean, Gammarus pulex, 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 Echinorhynchus angustatus 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 £. 
proteus, 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 aso-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 
