202 CRUSTACEA. 



the tail, or the middle one of its terminal fin, is transversely divided 

 by a suture. The 



Astacus communis ; Cancer astacus, L. ; Roesel, Insect., Ill, 

 liv, vii. The Craw-Fish 1ms its anterior forceps granulated, and 

 the inner edges finely dentated. There is a tooth on each side 

 of the snout, and two at its base ; the lateral edges of the seg- 

 ments of the tail form an acute angle. Its colour, which is 

 usually a greenish brown, is sometimes altered by accidental 

 circumstances. 



This species, which inhabits the fresh waters of Europe, has 

 been more particularly studied, both as respects its anatomy 

 and habits, and the faculty enjoyed by the Crustacea of regene- 

 rating their antennae and feet when they are either mutilated or 

 destroyed. When about to cast its shell, two stony concretions 

 are found in the stomach, formerly much used in medical prac- 

 tice as an absorbent, but now replaced by the carbonate of mag- 

 nesia. It conceals itself in holes, or under stones, never quitting 

 its retreat except to search for food, which consists of small 

 Mollusca and Fishes, and the larvoe of Insects. It also feeds on 

 putrid flesh, the carcases of quadrupeds, for instance, which 

 are placed as a bait for them in nets, or in the centre of fagots 

 of wood. They are also taken in their holes by the light of 

 torches. It changes its shell towards the end of spring. Two 

 months after coition, which takes place ventribus junctis, the 

 female produces her ova, which are at first collected in masses, 

 and glued to the false feet, by means of a viscid humour. They 

 are of a reddish brown colour, and enlarge before they are 

 hatched. The young Astaci, at first extremely soft and precisely 

 like their parent, shelter themselves under her tail, and remain 

 there several days, until their bodies acquire a certain degree of 

 solidity. 



The term of existence assigned to the Astaci seems to be 

 twenty years and upwards, their size augmenting in proportion 

 to their age. Those are preferred for the table which inhabit 

 running streams of fresh water. A parasitic animal belonging 

 to the Anneli:les 5s found on their branchiae, long ago observed 

 by Roesel, but imperfectly known until the researches of M. 

 Odier *. 



The fresh- waters of North America produce another species, 

 the A. Bartonii, figured by Bosc. Hist. Nat. des Crust., II, 

 x, 1. 



A third inhabits the rice-fields of the same country, to which, 

 according to Major Le Contc, one of the best naturalists of the 

 United States, it is very injurious. 

 In the fourth section, that of the CARIDES, the intermedial antennae 



are superior or are inserted above the laterals : the peduncle of these 



latter is completely covered by a large scale. 



* See his Memoire sur le Branchioddle, inserted in the Mem. de la Soc. d'Hist. 

 Nat. tome I, p. 69, et seq. 



