560 SUMMARY OF CURRENT RESEARCHES RELATING TO 



found in the stomacli, and wliicli are probably the true excreta ; and 

 of niuch larger granulations formed of concentric layers, which seem 

 to be true calculi, which are formed not in the intestine, but in tubes 

 which open into it, and in which similar calculi are to be found. 

 These tubes appear to be Malpighian ; but the chemical examination 

 of the calculi is still to be effected. 



In conclusion, MacLeod throws great doubts on the exactness of 

 the descriptions of the skeletal part of Acarina as given by previous 

 writers, and promises to enter more fully into this subject. 



8. Crustacea. 



Sexual Colour-Variation in Crustacea.* — Differences in the 

 colour of the two sexes among Crustacea are of very rare occurrence. 

 Darwin in ' The Descent of Man,' chap, ix., says he is acquainted with 

 but two instances of this peculiarity : one in the case of Squilla 

 stylifera, and a second in a species of Gelasmus, or fiddler crab. H. 

 W. Conn records a third and very striking instance in Callinectes 

 (Neptunus) hastata, the common edible crab of the southern coast of 

 North America. There are a number of differences in the shape of 

 the two sexes, but besides these they present a marked difference in 

 colour. This colour-variation is confined to the first pair of thoracic 

 appendages, the pair bearing the large chelae. These appendages 

 are of a yellowish brown on the upper surface, a whitish yellow on 

 the outside, and of a brilliant blue on the inside and particularly at 

 those parts which are protected from the light when the appendage is 

 folded. It would seem therefore that this blue coloration was en- 

 hanced by not being exposed to light. The colour of different 

 individuals is tolerably constant and uniform. 



Between the colours of the male and female appendage considerable 

 differences are discernible. The most noticeable difference is that 

 the male appendage appears remarkably blue when compared with the 

 female. This is due partly to the fact that the amount of blue surface 

 in the male is much greater than in the female, and partly to the fact 

 that the blue colour is of a much more brilliant hue. The blue 

 colour in the male extends nearly to the tips of the two fingers of the 

 chelae, both the finger-like process of the propodite and the dacty- 

 lopodite being largely coloured blue. The extreme tips are, however, 

 of a brilliant purple. In the female these parts are of an orange hue, 

 with not a trace of blue about them. Its tips are also coloured 

 purple, but not so brilliant a purple as is found in the male. In the 

 male the blue colour extends partly upon the outer surface. In the 

 female it is confined to the inner surface and only extends to the base 

 of the dactylopodite. The outer surface of the dactylopodite and of 

 the finger-like process of the propodite are in the male white, while 

 in the female they are reddish orange. Upon the male appendage 

 there is no orange colour as a rule. 



These differences in colour are in all cases very marked, and will 

 always serve to distinguish a male from a female appendage. No 



* Johne-Hopkins University Circulars, iii. (1883) p. 5. 



