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



physiology. Attempting to explain phenomena to them isolated, 

 they were compelled to invoke the aid of some imponderable 

 agent, whether Final Cause, or heat, or some other: what fol- 

 lowed was the creation of dilemmas or contradictory proposi- 

 tions. In the present instance the same result is assigned to 

 three causes : solidification is, on the one hand, due to heat ; 

 where that is, by assumption, at a minimum, if not wholly ab- 

 sent, or where evaporation could not readily be supposed to take 

 place (as in the sea), original composition is appealed to ; in a 

 third passage, purpose is equivalent to cause. 



The general aspect of the group presents two marked features, 

 not given as grounds of division, but merely stated as differences : 

 namely, the body of Carcinus is rounded, that of the other genera 

 long (H. An. iv. 2. 5) ; the former is tailless, the latter have a 

 tail with appendages, whose function as an organ of locomotion 

 is so important that its use for the reception of ova does not 

 seem to have suggested the analogy to that part in Carcinus 

 employed for the same purpose. The congress of these animals 

 could scarcely have been witnessed by Aristotle himself; otherwise 

 the extension of the operculum and exposure of its appendages 

 would doubtless have suggested its true nature to so acute an 

 observer. 



The carapace of Carcinus is " the case of the body, one, un- 

 divided, answering to the head and all other parts." In the 

 Macrura the nomenclature is not fixed : thorax is the designa- 

 tion of all covered by the buckler, though there is no resem- 

 blance between this part and the similarly named cavity of 

 Vertebrata, the function and organs of respiration throughout 

 the class being alike unknown to Aristotle. The tail includes 

 all posterior to the thorax ; its lower surface is sometimes called 

 abdomen. The terms ovpd, nepKos, and 6 rpd^rjXo^ Kakovfx,evo<i, 

 the so-called neck (probably a popular phrase), are used indiscri- 

 minately. In describing the mechanism of oviposition (H. An. v. 

 15. 2), the intervals separating the abdominal segments from the 

 thorax and telson (/cep/cos) are mentioned ; but a threefold divi- 

 sion is not intended, since the telson of Astacus is called the 

 sixth segment of the "neck." Cuvier found, in rj /cep/co?, inepv^ia 

 Se Trevre, of Carabus, rj ovpd koX 7TTepv>yia reaaapa of Caris, 

 indications of structural difference ; but the expressions are 

 synonymous. The use of the tail as a swimming-organ is of 

 course noted, and mentioned as a very important distinction 

 between the kinds of Malacostraca (H. An. i. 1. 8). It is absent 

 in Carcinus, because it would be useless to an animal whose only 

 mode of progression is ambulatory (De Part. iv. 8). The de- 

 pendence of structure upon function is stated twice afterwards 

 in the same chapter. The reasoning is in accordance with that 



