NOTES ON BOPYRUS SQUILLARUM. 27 



excresceuces on the under side margins of the tail. Benoatli 

 the plates coveriuf; these the male is usually found. Fig. 4 

 exhibits the male in i^itu. The colour of the female Bopyrus 

 is pale green, and the body is not of strong consistence. The 

 young Bopjiri are of an oval form, somewhat like a wood 

 louse, with the outer pair of antennae greatly elongated, carrying 

 slender setae. The legs are sub-chelate, and the tail carries two pairs 

 of joints, terminating in setae. It appears that in the nauplius or 

 larval condition (Fig. 5), the young exhibit the most advanced stage 

 of development ; according to Spence Bate and Westwood. " the 

 organs of sense aud motion being proportionately larger and better 

 developed at that period of their existence than ever after." Messrs. 

 Spence Bate aud Westwood further say: "It would thus appear as if 

 the nervous energy was then greater, and that the growth of males 

 aud females is but what Dr. James D. Dana calls a vegetative process, 

 and one that is destructive of cephalisation, which decreases in 

 proportion to the growth of the animal. They therefore argue 

 that of the adult Bopi/ri the smaller male ought to be taken as typical 

 of the species rather than the more abnormal female." I particularly 

 direct your attention to the fact of high development in the nauplius 

 stage as a most remarkable illustration of that special branch of 

 modern biological speculation termed phylogeny, which professes 

 " that the development of any organism should furnish the key to its 

 ancestral history."* It would appear from this that Bopyrus is derived 

 from some more perfect form of crustacean, and that its degraded 

 organs in the female in maturity are due to its peculiar environ- 

 ment within the carapace of the prawn. The Bopyri seem to gain 

 access to the bodj' first by sheltering in the early stage among the 

 freely hanging ova of the prawn. They work in pairs, as appears from 

 a communication to the Proc. Zool. Soc, November 24, 1863, after- 

 wards finding their way into the carapace, and so, as the authors I 

 have quoted say, " having quitted the care of their own parent they 

 are foster el by another on whom probably at a later period they prey 

 parasitically." As with most parasites the fecundity of these 

 creatures is considerable, no fewer than 800 young being nourished in 

 the incubatory pouch of the female. Most of these perish, for only 

 one mature parasite and its mate infest their host at one time. 



The question has been asked as to what becomes of the parasite 

 during the periodic moults of its host. I have not been so fortunate 

 as to take a prawn in this condition infested with Bopyrus, but I 

 apprehend that the number and strength of the well-hooked hands are 

 quite sufficient to retain the female parasite in position during the 

 moulting process of its host. Another interesting question suggests 

 itself. What becomes of the exuvium of Bopyrus during its period of 

 moulting, and in what way is this removed ? Does it disappear only 

 during the moulting process of the prawn ? 



* Vide " A Manual of the Anatomy of Invertebrated Animals." By T. H. 

 Huxley, LL.D., F.R.S., 1877, lutroductiou, page 41. 



