Outline of Life-history 



Parasites. 



observe tliis ; he found tliem abundant at low- water 

 mark in Salem harbour ; Verrill dredged one from 

 a depth of twenty fathoms at Eastport, Maine ; and they 

 have also b9en found on the coasts of Denmark ^ 

 Swainson has found them in the sea at the Mumbles, 

 Swansea, and has dredged them in fifteen fathoms off the 

 Isle of Man. At Sheerness they inhabit salt-marshes, 

 which are overflowed by the tide every day. 



As might be expected from its place of abode and the 

 nature of its food, the blood-worm is much infested by 

 parasites. Stalked infusoria attach themselves to its 

 head as well as to other parts of the body ; nematoid 

 worms coil themselves up in the body-cavity, and even 

 distend the whole integument ; Gregarines lurk in the 

 intestine. According to Villot ^ a species of hair-worm 



Fig. 2. — Gordian worm, infesting larva of Cliironomiis. i, immature female, 

 from larva, y^, in. long. 2, adult male, from mud of stream, about i in. long. The 

 adult female has no spicule, and the genital orifice is >3 of the leng-th of the body 

 from the head end. 



(Gorclius), while still of microscopic size, bores into the 

 Chironomus-larva, and becomes encysted within it. If 

 the larva is swallowed by a fish, the Gordius is set free; 

 it now fastens upon the mucous lining of the intestine 

 of its new host, and again encysts itself. AVhen it has 

 grown to its full size, it escapes into the water, elongates 



1 Meinert, 1886, ji. 73 ; Packard, 1870 ; Monnier, 1874. 



2 Yillot, 1874. 



