ANIMAL KINGDOM. 



115 



Fig. 45. 



cles (e e} along with the ductus communis 

 choledochus (/'). The cartilaginous plagi- 

 ostome fishes, the most complicated of this 

 class, have a conglomerate form of the pan- 

 creas opening in the same situation. In the 

 sturgeon and in the sword-fish an interme- 

 diate form is seen between the simple pan- 

 creatic follicles of the invertebrated classes 

 and the more complicated conglomerate organ 

 in the higher vertebrata. This is shown in 

 the annexed figure of the chylopoietic viscera 

 as I found them in the xiphias gladius (jig. 

 46), where the liver () is raised up -to show 



Fig. 46. 



the three hepatic ducts uniting with the cystic 

 from the curved gall-bladder (c) to form a very 

 short ductus cotnmunis choledochus. The 

 pancreas (d) forms a large reniform mass com- 

 posed of numerous straight follicles produced 

 by the successive divisions of the great termi- 

 nal duct (e) of this organ. This large inter- 

 mediate organ is surrounded with a distinct 

 muscular tunic to force its contents into the 

 duodenum immediately beyond the pyloric 

 valve (b). The tortuous small intestine ends 

 by a valvular orifice (f) in a very short but 

 distinct colon, which presents no ccecum in its 

 course to the anus (g). The bilocular heart 



of fishes is entirely branchial ; it is often pre- 

 ceded by a sinus venosus, and is always 

 succeeded by a butbus urttriusus, which often 

 presents numerous internal valves in its course. 

 The venous blood is entirely sent through the 

 gills, and the branchial veins, after giving 

 branches to the anterior parts, unite to form 

 the aorta which sends the arterialised blood 

 through the rest of the system without the aid 

 of a systemic heart. The respiration is effected 

 by the transmission of water through the mouth 

 or through distinct spiracula, and over the 

 surface of the branchiae, which are internal in 

 the adult, and are often preceded by external 

 branchiae in the young. The lungs are always 

 rudimentary, when present, sometimes in form 

 of a shut single air-bag, sometimes divided 

 or ramified, and most generally communicating 

 by a ductus pneumatic us with the intestine or 

 stomach, or oesophagus, but seldom employed 

 for respiration. Fishes are oviparous and have 

 the sexes separate ; the ovaries are continuous 

 with the oviducts in osseous fishes, and de- 

 tached from them in the plagiostome chon- 

 dropterygii, and impregnation sometimes takes 

 place internally and sometimes after the ova 

 are separated from the body. (See PISCES.) 



20. Amphibia, cold and red-blooded, verte- 

 brated, oviparous animals, with three cavities of 

 the heart, with a naked skin, and breathing, in 

 the young state, by gills. These animals com- 

 mence their career like fishes with one auricle 

 and one ventricle, which send the whole of the 

 blood through the branchiae, and they have at 

 this period also double concave bodies of the 

 vertebrae, as in fishes. Many retain the gills 

 through life, accompanied with pulmonic cavi- 

 ties, from which the arterialised blood is sent to 

 a small left auricle. These animals are termed 

 amphibia from the metamorphosis to a terres- 

 trial from an aquatic life seen in most of the 

 species. Their skeleton is imperfectly con- 

 solidated, their ribs very short or wanting, their 

 pelvic arch free or nearly so, and their atlantal 

 and sacral extremities often very imperfectly 

 developed or partly deficient. Their toes are 

 destitute of claws, as their skin is of scales, 

 and the respiration through their naked, highly 

 sensitive, and secreting surface compensates for 

 the imperfect development or limited use of 

 their lungs, especially during submersion or 

 hyber nation. Some reside constantly in the 

 water, others occasionally, and others continue 

 on land. The male organ of intromission is 

 rarely developed, and impregnation of the ova 

 is generally effected externally. The genital 

 organs are double and symmetrically developed 

 in both sexes. The perennibranchiate amphi- 

 bia, especially the axolotl, have been shown by 

 Weber to possess a double auricle like the 

 caducibranchiate species. (See AMPHIBIA.) 



21. Reptilia, cold and red-blooded, ovipa- 

 rous, vertebrated animals, with two auricles 

 and one ventricle, not breathing by gills in 

 their young state, covered with scales, and with 

 the means of internal impregnation. These 

 animals, whether aquatic or terrestrial, breathe 

 only by means of lungs, and their pulmonic 

 respiration and the left auricle of the heart are 



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