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



abdominal appendages are considered equivalent to the thoracic 

 limbs. The motion of the feet is lateral, like that of the legs in 

 insects : progression by their aid is diagonal, as in quadrupeds, 

 in whom, however, two alternate and opposite feet precede the 

 corresponding members of the pair to which each belongs; 

 while in Carcinus the alternation is by four feet at a time (H. 

 An. i. 5. 7; De Inces. An. 14). The posterior feet of the small 

 semiparasitic Carcini are flat, " so as to be useful for swimming" 

 (De Part. iv. 8). The oblique motion of the pincers is adapted 

 for conveying to the mouth the food grasped by them. Those 

 of Astacus are minutely described, and the tooth-like arrange- 

 ment of the tubercles suggests their comparison with jaws, of 

 which the upper is moveable, the lower fixed. The absence of 

 pincers in Carides is attributed to the number of the other feet, 

 on which the material is used up. This number is in conse- 

 quence of their natatory habits — doubtless a reference to the flat 

 tips on the majority of their limbs. The teleology of this chapter 

 (De Part. iv. 8) has already been spoken of: in the last quota- 

 tion we find another instance of the law of economy which 

 Aristotle had stated long before the time of Geoffroy St.-Hilaire, 

 by which he explains the small tail of the bear, &c., and of 

 which he makes a more correct use in his acute explanation of 

 the mutual relations between fat and sperm (De Part. ii. 5). 



The description of the abdominal appendages is very obscure. 

 The hairy plates, irka/cas, to which the ova are attached are said 

 to be four in Astacus. Did the position of the first pair nearer 

 the middle line than the others exclude them from the reckon- 

 ing ? In Hist. v. 15 they are said to accompany each somite of 

 Carctbus, and are therefore five. It is they probably, not the 

 ova, which are meant as being largest in the middle, the last 

 being the smallest (H. An. v. 15. 2). This version is in accord- 

 ance with a previous passage, where the female is said to have 

 these appendages fieydXa tcah eV ekdrrov rd 77730? ra> rpa^rjXtp 

 (iv. 2. 5) : the clause which follows (6 o° dpprjv iXdrTO) feat ov/c 

 iiraWdTTOvra) is rejected as spurious ; it is, at any rate, un- 

 necessary, since the overlapping which it states to be absent in 

 the male is not properly opposed to any arrangement in the 

 female, the present chapter (v. 15) denying it in her also. If, 

 therefore, the clause is retained, iiraWdrTovTa must be read 

 en-' ekdrrov. 



The cloacal office of the anus is stated clearly (De Gen. i. 15) : 

 " In the Malacostraca and the like, the passage for excrements 

 and the uterine duct is the same : it is by this passage that the 

 seminal fluid is discharged." It is this sentence which makes 

 intelligible the remark that the ova are not continuous with the 

 duct, but are on the middle of the body, which is separated by 



