254 Dr. J. Young on the Mahcostraca of Aristotle, 



chance of escaping destruction necessitates their extrusion in 

 an imperfect state; for were they to be retained till mature, 

 their number would be diminished and their chances of destruc- 

 tion increased. To this end also is adapted their rapid develop- 

 ment when without the body, as they thus more speedily over- 

 pass the precarious age (De Gen. i. 8). Again, the eggs of birds 

 acquire their hard covering on the cessation of growth ; those 

 of cartilaginous fishes remain soft because the parent body has 

 not sufficient warmth to dry up the outer covering {ibid. 10). 

 In Malacostraca no period is assigned at which the shell ac- 

 quires its density ; on the contrary, growth advances, even though 

 the shell is hard. Again, the relation established between the 

 outer covering and that of the egg (DeGen.ii.l), though perfectly 

 applicable to the Malacostraca, fails utterly in other groups of 

 animals, and is at variance with the teleological speculations 

 just stated. But, contradictory as are these statements, it must 

 not be forgotten that the facts are themselves no less puzzling. 

 The true theory of generation is only of late and very slow 

 growth. How nearly the searching intellect of Aristotle ap- 

 proached that theory may be seen in Lewes's masterly sketch of 

 its history. The reader will there find proof of the wonderful 

 sagacity Aristotle showed in his observation and reasoning re- 

 garding embryology in beings less obscure than the Malacos- 

 traca, whose eggs he was entirely destitute of the means of 

 properly studying. 



Such is the account given by Aristotle of the anatomy of 

 Malacostraca. The facts are few, obscurely stated, sometimes 

 erroneous : they are all such as could be obtained by simple in- 

 spection : dissection there was none. For the genital passages 

 are not traced to their terminations, but are lost sight of where 

 they dip to reach the external apertures ; their further course is 

 guessed, and guessed wrongly as towards the tail. The muscles 

 are not mentioned ; for if these organs were not understood in 

 the Vertebrata, much less would they be intelligible in these 

 animals; they are probably the pale substance of which he 

 speaks. An omission more remarkable is that of the power 

 possessed by these animals of reproducing lost parts — a fact 

 which seems also to have escaped the notice of the fishermen 

 from whom he derived so much information. 



It has been conjectured that Aristotle had a more extensive 

 knowledge than his anatomical statements indicate. That he 

 knew more species than he has named is very probable ; but we 

 may safely assume that, in treatises looking at structures from 

 difterent points of view, he has made use of all the structural in- 

 formation he possessed. It must be remembered that the main 



