COMPARATIVE ANATOMY. 



the tame animal these proportions are as 

 thirteen to one. In the domestic cat, five 

 to one ; in the wild cat, three to one ; 

 in the bull, twenty-two to one ; in the 

 buffalo, twelve to one. They are, on the 

 contrary, longer in the wild than in the 

 tame rabbit ; the proportions in the for- 

 mer being eleven, and in the latter nine 

 to one. 



The proportion of the intestinal canal 

 to the length of the body, in birds, is as 

 two, three, four, or five to one. It is not 

 ahvays longest and largest in the grami- 

 nivorous species, as many piscivorous 

 birds have it equally long. 



It is hardly twice the length of the body 

 in many reptiles ; and not so much in the 

 frog, although it is nine times as long as 

 the space between the mouth and the 

 anus in the tadpole. 



The alimentary canal of some fishes is 

 continued straight from the mouth to the 

 anus, and does not, therefore, equal the 

 length of the body. The lamprey, skate, 

 and shark, are thus circumstanced. 



Most birds have two cseca, which are 

 longer in the gallinae than in the carni- 

 vorous tribes. The rectum ends in a part 

 called the cloaca, which is a large mem- 

 branous bag, containing also the termina- 

 tion of the ureters, that of the oviduct, 

 the vasadeferentia, and of a membranous 

 bag of unknown use, called bursa fabricii. 

 This also holds the penis, where there is 

 one. 



A1IMEKTART CAITAL OF THE LOWER 

 ORDERS. 



The simple globular hydatid, which is 

 frequently found in the different viscera 

 both of man and quadrupeds, has been 

 supposed by some to be an animal con- 

 sisting entirely of a stomach. Doubts, 

 however, have been lately raised, whether 

 or no this be really an animal. Even if 

 it were allowed that these bags are ani- 

 mals, it does not follow that their cavity 

 is a stomach ; and the attachment of the 

 young to the sides would rather justify 

 us in considering it as the organ of gene- 

 ration. 



The hydatid, which is more frequently 

 found in animals which possess a head 

 and mouth like the taenia, enabling it to 

 attach itself to parts, and which can be 

 seen to move when placed in warm water, 

 is generally allowed to possess an indepen- 

 dent vitality. But whether the bag of 

 water, which forms its body, be a sto- 

 mach, is certainly doubtful. 



The most simple form of an alimentary 

 cavity exists in the common fresh water 



VOL. III. 



polype (hydra). It appears to be exca- 

 vated in the substance of the body, and 

 has a single opening situated in the cen- 

 tre of the space surrounded by the ten- 

 tacula. The nutritive matter soaks im- 

 mediately into the body, and imparts its 

 colour to the animal. 



The large masses of gelatine, called 

 medusae, which resemble in form mush- 

 rooms, and are found floating in the sea, 

 have a somewhat similar structure. A 

 stomach is hollowed out in the pedicle ; 

 and vessels, commencing from its cavity, 

 convey the nutritious food over the body. 

 Sometimes the stomach has a simple open- 

 ing ; in other cases there are branching 

 tentacula, on which canals commence by 

 open orifices ; these unite together to 

 form larger tubes, and the successive 

 union of these vessels forms at last four 

 trunks, which open into the stomach, and 

 convey the food into that cavity. This 

 very singular structure constitutes a re- 

 markable analogy to the roots of trees ; 

 and Cuvier has formed a new genus, 

 under an appellation derived from this 

 comparison, viz. the rhizostoma, from 

 c f'(f> a root, and /", a mouth. 



The star-fish (asterias) has a membra- 

 nous cavity in the centre of its body, 

 communicating externally by a single 

 opening ; two canals extend from this into 

 each of the branches, or, as they are some- 

 times called, the fingers of the animal, 

 where they subdivide and form numerous 

 blind processes. 



The tape-worm (taenia) has a small ca- 

 nal running on each side of its body ; the 

 two tubes are joined together by trans- 

 verse productions at each joint. 



The ascaris lumbricoides (round-worm) 

 has a simple canal running from one ex- 

 tremity of the body to the other. 



The leech (hirudo sanguisuga, or me- 

 dicinalis) has a short oesophagus and a 

 very large stomach, divided by nume- 

 rous membranous septa, which are per- 

 forated in the centre. It has been ge- 

 nerally supposed that this animal has no 

 anus ; but Cuvier says that it possesses 

 a very small one. Lemons d'Anat. Comp. 

 torn. iv.p. 141.) Dumeril, on the contrary, 

 denies its existence. (Zoologie Analyti- 

 que, p. 298.) 



The common earth-worm (lumbricus 

 terrestris) has a long canal, divided by se- 

 veral partitions. 



The aphrodite aculeata has an intestine 

 running according to the length of the 

 body, and sending off on each side seve- 

 ral blind processes, which enlarge at their 

 termination. 



Jt r 



