222 the president's address. 



its temporary host in the Trichodectes of the dog ; and probably 

 there are plenty of instances amongst the entozoic worms. 



Another dipterous parasite, which is amusingly quick in the 

 ways of the world, is the Tachinaria. The fossorial Hymenoptera 

 lay their eggs in burrows, and providently provide a store of the 

 living larva) of other insects, which they bury for their young to 

 eat when hatched ; but while the prudent mother is thus engaged 

 the Tachinaria slips into the burrow, lays its eggs on the pro- 

 visions, and departs. The dipterous larvse are hatched first, so 

 that before the young bee or wasp is born its larder is emptied, 

 and the thief has gone forth rejoicing in its ill-gotten goods, and 

 leaving its Hymenopterous neighbour to starve. Some of the 

 Hymenoptera, however, are not easily excelled in the ingenuity of 

 their parasitism. Mr. Enoch has often shown us his skilful pre- 

 parations of the beautiful little Polenema ovulorum, which lays its 

 eggs inside those of the common Cabbage- Butterfly. This charm- 

 ing little atom has a relative very like it, which has managed to 

 adapt its fragile wings, with their long fringes, to an aquatic, or 

 semi-aquatic, life ; and lays its eggs inside those of the beautiful 

 dragon-fly, Agrion virgo. 



The crustacean parasites are very remarkable. It is chiefly 

 among them that there occurs that strange form of parasitism — 

 that while the female is a true parasite upon another animal, the 

 male is practically parasitic upon the female ; but, on the other 

 hand, in Nicothoc, where the female has become a mere bunch of 

 digestive and reproductive sacks, the male is a free-swimming 

 creature. This degeneration of the female parasite into little more 

 than an egg-sack is very remarkable amongst crustaceans, but is 

 by no means confined to them ; the same thing occurs with the 

 mollusc Entoconcha and other creatures. Among strange crusta- 

 ceans may be mentioned an Isopod Bopyrus, the female of which 

 lives under the carapace of the prawn, the male being free, &c. ; 

 the Phryxus paguri discovered by Eathke, the female of which is 

 found attached by its back to the abdomen of the Pagurus, thus 

 sharing the shelter of the shell which the latter has taken posses- 

 sion of. The male of this creature is one of those that is parasitic 

 upon the female. Another Isopod, the Cymotliue, lives in pairs, 

 male and female, in the bucal cavity of fishes {e.g., the Stromatea) , 

 not to devour its host, but to share his dinner. Those that live in 



