ANIMAL KINGDOM. 



117 



generally unsymmetrical in their development 

 in the female. The testes are internal, and the 

 vasa deferentia terminate in the cloaca, where 

 there is sometimes a grooved organ of intro- 

 mission. In the female the left ovary and 

 oviduct are developed, the right for the most 

 part atrophiated and useless. The cavity of 

 the cloaca in most birds, as seen in that of the 

 great condor of the Andes (fig- 49), receives 

 the end of the rectum (), which forms a wide 



Fig. 49. 



rectal vestibule (6) : beneath this lies the part 

 analogous to the urinary bladder (c d). Lower 

 than the urinary sac are found the two openings 

 of the ureters (// A), with the pervious oviduct 

 on the left side (./'), and the remains of the 

 impervious oviduct (g) on the right side. The 

 bursa Fabricii and the clitoris (when present) 

 are placed more posteriorly in the preputial 

 cavity. The most distinct forms of these gene- 

 rative and urinary parts, and the nearest ap- 

 proach to the mammalia are seen in the cloaca 

 of the ostrich (.//g. 50), where the rectum (a) 

 opens into a wide and distinct rectal vestibule 

 (6), which extends into a large urinary bladder 

 (rf). Beneath the urinary bladder is the ure- 

 thro-sexual canal (e), into which the two ureters 



Fig. 50. 



(h k h* A*) and the oviducts (//*/* #) P en 

 towards the dorsal and lateral part. The pre- 

 putial cavity (') is the terminal portion in which 

 the distinct clitoris is here lodged. The ova 



are impregnated internally, their chorion is 

 calcined, and their development is effected by 

 incubation. (See AVES.) 



23. Mammalia, warm and red-blooded ver- 

 tebrata, having four cavities of the heart, with 

 a viviparous mode of generation, and possessing 

 mammary glands ; with the lungs free in a 

 distinct thoracic cavity, and generally having 

 the body more or less covered with hair. The 

 bodies of their vertebra unite by flat surfaces, 

 the tympanic bone is fixed, the jaws are gene- 

 rally furnished with teeth lodged in deep alveoli, 

 the coracoid bone rarely reaches the sternum, 

 and the posterior extremities, when present, are 

 always attached by the pelvic arch to a solid 

 sacrum. The thoracic and abdominal cavities 

 are separated by a muscular diaphragm. The 

 hemispheres of the brain contain large ventri- 

 cles, and rarely want convolutions, the optic 

 lobes are small, concealed, solid, and divided 

 by a transverse sulcus, the commissures of the 

 brain and cerebellum, and the hemispheres of 

 the cerebellum are large. The alimentary 

 canal is of great length, the colon long arid 

 wide, with a single crecum, and sometimes 

 with a vermiform appendix, and the anal open- 

 ing is generally distinct from the urinary and 

 genital passages. The tricuspid valve is thin 

 and membranous, the aorta descends on the 

 left side, there is no inferior larynx, the epi- 

 glottis is distinct, and the bronchi continue 

 cartilaginous into their ramifications in the 

 lungs. The lungs, generally divided into lobes, 

 move freeely fn a distinct thoracic cavity, and 

 have no abdominal cells or perforations on their 

 surface, as in birds. There is always a urinary 

 bladder, and the urethra in the male passes 

 through a tubular penis. The organs of gene- 

 ration are double in both sexes, symmetrical in 

 the male, and rarely unsymmetrical in the 

 female. The oviducts commonly unite at their 

 lower part to form a uterus, in which the ovum 

 becomes again connected with the parent, and 

 is hatched. There are mammary glands open- 

 ing externally for lactation during the helpless 

 condition of the young. (See MAMMALIA.) 



These are the PRIMARY and SECONDARY 

 DIVISIONS of the ANIMAL KINGDOM, the strtic- 

 ture, classification, and history of which it is 

 proposed to consider in this Cyclopaedia, under 

 the heads of the several classes as enumerated in 

 the subjoined table. 



ANIMALIA. 



I. Sub-regnum, Cyclo-neura vel Radiata. 



Classis 1. Polygastrica. 



2. Porifera. 



3. Polypi fera. 



4. Acalephae. 



5. Echinoderma. 



II. Sub-regnum, Diplo-neura vel Articulate. 



Classis 6. Entozoa. 



7. Rotifera. 



8. Cirrhopoda. 



9. Annelida. 



10. Myriapoda. 



11. Insecta. 



12. Arachnida. 



13. Crustacea. 



