NOTES ON BOPYRUS SQUILLARUM. 275 



in " the struggle for existence." Many littoral marine animals of 

 high type, as crustaceans and fishes, frequenting a varying environ- 

 ment, appear to have acquired a superiority of intelligence over those 

 confined to deep water where the conditions of life remain unchanged. 



In the '-Principles of Biology," and in that division of it which 

 treats of the morphological development and of the general shapes of 

 animals, Mr. Herbert Spencer has pointed out, inter alia, that the struc- 

 ture of decapodous crustaceans, as represented by the prawn, exhibits 

 an advance in structure over the isopodous crustaceans, and a marked 

 advance over such creatures as the centipede and julus types, 

 any one of which latter animals (all the segments being nearly 

 uniform) may be bisected transversely into parts differing very 

 slightly from each other; but if cut in two horizontally the 

 under and upper halves are decidedly unlike, whereas the head 

 and tail of the prawn show a very marked contrast and an 

 advance in structure over the other segments. Of bilateral 

 symmetry, and in comparative harmony with the environment, the 

 incidence of forces being equal, the common prawn exhibits a 

 striking contrast to Bopyrus as will hereafter appear. Doubtless "the 

 sum of the vital activities " of the prawn, as Mr. Herbert Spencer 

 would express it, is much greater in any given interval than that of 

 many members of its own class, and greater even than animals of 

 higher type, such as the oyster and others, which lead sedentary lives. 



In Bopyrus, what first strikes one as being noticeable is an absence 

 of the symmetrical arrangement of Pahemou, which characterises the 

 female Bopyrus, giving a strange lop-sided appearance to it 

 (Fig. 2), although the male (Fig. 3), being free, is symmetrical. 

 From the peculiar position of the female in the carapace of the prawn 

 the incidence of forces is unequal. Next is the disparity of 

 size between the sexes, the female being about five times 

 longer than the male, which is only one line in length. This 

 rule obtains sometimes in the Insecta, but not markedly so in the 

 higher Crustacea. The female of Bopyrus is broad and ovate, while 

 the male is elongated. Further, the segments of the body of the 

 female appear but faintly, those of the male on the contrary being 

 well marked and distinct. The head (cephalon) is almost immersed 

 in the body of the female, but is better developed in the male, the 

 eyes appearing distinct. The antennae in both sexes are very short 

 and rudimentary, and so is the mouth, which, according to Spence 

 Bate and Westwood appears to lose much of its normal character, 

 and as one would expect from the parasitic nature of Bopyrus, fulfils 

 the office of a sucking apparatus. The seven pairs of legs are almost 

 of equal size, strong and thick, and furnished with a well-developed 

 broad hand, strongly hooked for prehension. The tail (pleon) 

 is well marked in both sexes. The females are furnished with 

 large incubatory plates. Not only in Bopyrus, but throughout the 

 curiously degraded family of the Bopyridse, the branchial organs 

 "are depauperated to the lowest degree," being little more than 



