73 



attached, must draw her nourishment tr-oui the liost iu order to be able to grow to a bulk 

 which, adding its own volume after having finished laying eggs, to that of the eggs it has 

 produced, is frequently hundreds of times larger than tlie volume of the larva at the time 

 when it attached itself, and after having fixed itself it is impcjssible for the animal to 

 procure the nourishment necessary for tliis enormous growth in any other way than by a 

 hole worked through the comparatively solid skin of the host, whose blood must form the 

 food of the parasite. 



Hereby we have found a fixed starting-point in this question, and it is more than 

 probable that the females of all the other Choniostomatidae also grow and nourish themselves 

 by sucking the blood of their host through a hole they have gnawed. At the same time, it 

 seems rather probable that the females of many of these species, either voluntarily or invo- 

 luntarily, e. g. by presslue of another specimen, or by the bulk of ovisacs, are pushed out 

 of their place and have to gnaw a new hole for themselves. I have frequently found a 

 female in such an attitude relatively to some of the ovisacs it had laid, or the ovisacs 

 arranged in such a manner as to make me suppose that the animal had changed place. 



How fai- the males of this family take food, I do not know, but as their mouth is 

 as well developed as that of the females, it seems likely that they do it while young, and 

 perhaps not when they are old (about theii- growth, s. above on pag. 57 — 58). I consider it rather 

 doubtful whether the larvae take food, but I am quite certain that the pupae, wliich are 

 provided with a mouth, and about whose considerable growth several facts have been stated 

 above, nom-ish themselves in a way similar to that of the females. 



h. The Influence of the Parasites on their Hosts. 



Giard and Bonnier have proved that parasitic Crustacea of diflerent groups (as 

 Entoniscinae , Eliizocephala) cause a »castration parasitaire« in their hosts. In the last of 

 their papers quoted above they mention Delia Valle's untenable hypothesis that SpJiceroneJla 

 eats the eggs of its host, and they maintain that tliis suggestion is wrong, and that this is 

 also a case of »casti'ation parasitaire«, after wliich they continue: »Dans des cas tres rares, 

 I'hote ayant 6t6 infests tardivemeut, cette action [namely the castration] ne s'exerce pas 

 aussi 6nergiquement, et quelques oeufs peuvent etre pondus et fecond6s, comme nous I'avons 

 vu une fois chez Clypeoniscus [a genus belonging to Epicaridea wliich they have treated in 

 the same paper, and which they use as example and parallel], mais ce sont la des exceptions. 

 En g6n6ral, I'hote est infeste avaiit qu'il ne soit arriv6 a I'^tat adulte. Sous I'influence du 

 parasite, son d^veloppement genital est arrets sans que la croissance discontinue, de sorte qua 

 r^poque oil devrait se produire normalemeut la maturity sexuelle, la prog^niture legitime 

 est remplac6e par le parasite et les embryons de celui-ci«. This explanation, on the whole, 

 agrees well with the numerous data which I have given above on p. 65- 68 in the division 

 about the age and sex of the hosts, from my observations about my tliiity - eight species 



10 



