CRUSTACEA. 



773 



Fig. 412, Ventral aspect of the cephalo -thoracic portion of the 



Dichelestion. 

 a, trunk or sucker j 6, maxilla?. 



Fig. 413, The trunk or sucker magnified, 

 a, thelabrum; b, the mandibles. 



Fig. 414 Sf 415, The maxillae. 



Kg. 412. Fig. 413. JFig.414. Pig. 415. the anus, always separated 



from each other by the whole 

 length of the body. 



The mouth is the mere an- 

 terior and outward expansion 

 of the oesophagus ; it is fur- 

 nished with nothing that can 

 properly be compared to a 

 tongue; the horny and la- 

 mellar organ which writers 

 have sometimes spoken of 

 under this name is nothino- 

 more than the lower lip) 

 which has already been de- 

 scribed. 



The oesophagus itself is 

 short ; it rises vertically and 

 runs to terminate directly in 

 the stomach. Its general 

 structure, as well as that of 

 the stomach and whole of 

 the intestinal canal, bears a 

 very close resemblance to 

 what we observe among the 

 superior animals. They each 

 consist of two membranous 

 layers separated by one of 

 muscular fibres, always of 

 nultimate articulation (the daws, pincers, or greatest thickness in those points in which the 

 cheliferous extremities). most energetic contractions take place, and 



The extremity occasionally terminates in two especially at the entrance into and passage 

 articulations presenting no kind of unusual out of the stomach. 



development, but the last of which, termi- The stomach is of a globular form, and of 

 nated by a sharp point and armed with teeth very great capacity ; it fills a considerable 

 or serrae, returns upon the preceding one, so extent of the cephalic cavity, and presents two 

 as to form a kind of hook or pincer, opening portions very distinct from one another; the 

 in the opposite direction, (the sub-cheliform cardiac region, vertically surmounting the 

 extremities of the Squills and Crevettina;). mouth and oesophagus, the axis of which is 

 Lastly, these extremities frequently terminate lost in its own ; and the pyloric region, situ- 

 in a simple acute angle of which the animal ated behind the former, and forming a right 

 can make no use save in locomotion. angle with it. 



In the Sucking Crustacea, which live parasi- But the most remarkable feature presented 

 tically on other animals and feed by sucking by the stomach of the Crustaceans is the very 

 their blood, the structure of the oral apparatus complex masticatory apparatus it contains, 

 is extremely different.* Certain pieces which This consists of a considerable number of 

 must be considered as analogous to the labium pieces, the form and disposition of which vary, 

 and languette, are elongated, so as to form a and are always singularly in harmony with the 

 trunk or cylindrical tube, of variable length, kind of food taken and the general habits of 

 adapted for sucking, and in the interior of these animals. The apparatus, as well from 

 which are lodged the mandibles, now pro- the important office it fulfils, as from its 

 longed so much that they form two slender being no where else encountered in so perfect 

 and pointed processes the extremities of which a state of development, were worthy of a 

 serve as a lancet. The appendages which in description which would swell this article to 

 the masticating Crustacea constitute the jaws, too large a size; we shall therefore be brief, 

 here continue rudimentary, and the three pairs and merely state generally that it consists of a 

 of limbs which in the Decapoda complete the great number of pieces, so connected as to 

 oral apparatus, under the name of maxillary constitute a kind of solid frame armed in- 

 extremities, are here transformed into organs ternally with tubercles or sharper teeth situated 

 of prehension, of different forms, by means around the pylorus, and capable of being 

 of which the parasite attaches itself to its moved so as to bruise or tear in pieces the 

 victim. alimentary matters subjected to their action, 



In the whole of the Crustacea the intestinal and as they are about to pass through this 

 canal presents two openings, the mouth and opening.* 



The different pieces composing this appa- 

 ratus vary considerably in the different genera, 



* See our " Recherches sur 1'Organization de 

 la Bouche des Crustaces Suceurs," Ann. des Sc. 

 Nat. t. 28 ; Burmeister's Beschreibung einiger 

 iieuen schmarotzer Krebse, in the Acta Acad. 

 Caes. Leop. Nat. Cur. vol. xvii. p. 1. 



* Vide Cuvier, Le9ons d'Anatomie Comparee, 

 t. iv. p. 126, and Milne Edwards, Hist. Nat. des 

 Crustaces, t. i. p. 67, for further details. 



