Dr. J. Young on the Malacostraca of Aristotle. 253 



the Macrura it is effected in the same way as in retromingent 

 quadrupeds, the female raising the tail so as to bring the cloacse 

 in contact. The Carcini oppose the ventral surfaces, their oper- 

 cula being laid together. The prolongation of the act, which 

 permitted its being watched, is the result of their bloodlessness 

 and consequent cold habit. The necessity that the male secre- 

 tion should be applied to the eggs previously to extrusion leads 

 Aristotle to argue elaborately against the then alleged impreg- 

 nation of fishes by swallowing the male fluid, and even to doubt 

 the effusion of that fluid over the extruded ova. The pa- 

 rallel development of the secretions in each sex, and their simul- 

 taneous maturity, are sagaciously urged in support of his con- 

 jecture that congress takes place, though so rapidly as to elude 

 observation. The subsequent effusion over the ova would then 

 be a sort of economy by which the secretion is used up. As a 

 final proof that impregnation must take place during contact, 

 he points out the position of the eggs in Malacostraca beneath 

 the body of the female as rendering impossible any interference 

 on the part of the male. The " cold habit " of these animals 

 entails a dilemma for which he offers no explanation. Having 

 elsewhere stated that fish are of a cold habit, and here conjec- 

 turing a very short contact, he nevertheless attributes the pro- 

 longed contact of Malacostraca to the same thermal conditions. 

 His physiology was more correct than his metaphysical heat 

 theories. 



Gestation lasts for three months, in Caris four. After re- 

 maining attached to the female for about twenty days, the ova 

 are thrown off in a mass outwardly undivided. In fifteen days 

 more, the perfect individuals issue. The ova of this group are 

 not eggs in the true sense (H. An. i. 4. 1), nor are they scoleces, 

 but intermediate — a character they share with those of fish ; 

 and in both it is a result of " cold habit " (De Gen. i. 8). Their 

 development takes place after extrusion. They " are cooked " 

 in Crustacea while attached to the parent (H. An. v. 15. 4), the 

 evidence of which is their increase of bulk. This increase Lewes, 

 after Auber, attributes to endosmosis, if indeed it occurs at all. 

 The alleged imperfection of the Malacostracous egg seems to 

 be in great part an assumption demanded by the thermal specu- 

 lations so prominent in these treatises — to be, not observation, 

 but inference. It is not stated how the external hatching- 

 process conduces to a development which the internal warmth, 

 such as it is, is insufficient to mature. Having, however, 

 assumed the imperfection of the egg, it is necessary to explain 

 it. We have seen that it is the result of the cold nature of the 

 parents ; its purpose is to save the race from extinction : the 

 number of eggs required to be laid, so that some may have a 



