ZOOGENY. 387 



both organic kingdoms. It is probably also an imitation 

 of the five organs of sense. 



2217. The vessels of the branchiae of Fishes are 

 accompanied by bony rings, which correspond to the 

 feet of Crustacea. 



2218. All Fishes have, with few exceptions, five 

 branchial arches. 



2219. When in Fishes the sarcous system begins to 

 produce viscera, then the five branchial foramina pass 

 inwards, and only a single respiratory aperture is left for 

 them in the fleshy body ; namely, the external branchial 

 foramen. 



2220. In the lower animals water or air passes in and 

 out through the same respiratory aperture, but in Fishes 

 these two courses are preserved distinct ; for, except in the 

 Lampreys, the water enters through the mouth, and 

 passes out through the branchial aperture. 



2221. Here the attempt is manifested in a still greater 

 degree, to bring the process of respiration wholly under 

 the control of what is animal, this being in the next 

 place, and for the first time attained, when respiratory 

 apertures only are left upon the head. 



2222. The respiratory apertures of the head are the 

 nostrils, which are suddenly manifested in Fishes, but are 

 in them simply subservient to the sense of smell, and 

 not as yet to the respiratory act. 



2223. All the higher animals have, like fishes, bran- 

 chial apertures in the neck, only they coalesce and become 

 obliterated at an early period, or so soon as that respi- 

 ratory process appears, when air passes through the nostrils. 

 In the Salamanders and Frogs these branchial foramina 

 are persistent for a longer time, frequently through the 

 whole period of life ; but in Birds and Mammalia they 

 disappear, while they are in the embryo state. 



2224. When the branchial apertures close, the vessels 

 separate from the arches, and betake themselves to a 

 glandular body lying in front of them. The thyroid 

 gland is the remnant of the former branchial formation, 



