514 



ANATOMY OF VERTEBRATES. 



343 



One of the gills of the Newt, raagn. CCLXVIII. 



344 



loop, but speedily expanding, lengthening and branching into 

 lateral processes with corresponding looplets ; these blood-channels 

 intercommunicating by a capillary network, as at d, fig. 343. The 



gill is covered by ciliated 

 scales, ib. e, which change 

 into nonciliated epithe- 

 lium, f, shortly before the 

 gills are absorbed. 



The size of the gills is as 

 the proximity of their cleve- 

 loping vascular arch to the 



propelling organ of the 

 blood. In the Proteus 

 anguinus three pairs only 

 of branchial and vascular arches are developed, corresponding 

 with the number of external gills. In Siren lacertina, as in 

 caducibranchiate Batrachians, there are four pairs of branchial 

 arches ; the first and fourth being fixed, the second and third free : 



their contiguous borders on the 

 concave side are provided with 

 small interlocking processes. The 

 gills are in three pairs, increasing 

 in size, according to the above- 

 stated dynamic condition, from 

 the first to the third, which is 

 attached to both the third and 

 fourth arches : the upper or outer 

 surface is entire and covered by 

 ordinary integument ; the under 

 or inner surface is produced into 

 piniiatifid fringes, supporting the 

 capillary branchial vessels and 

 covered by thin epithelium. Each 

 gill is attached by its base an- 

 terior to and above the gill-slit, 

 which it overhangs. In the Axolotl, 

 fig. 344, the fringes of the gills are 



longer and more slender. In the 



& 



Menobranclms they resemble those 

 of the Triton. In the Siren, Pro- 

 teus, and Menobranclms the outer 

 gills are persistent, and, perhaps, 

 also in Axolotes. In each of these 



Circulating and respiratory organs, Axolotl, 

 Axolotes mexicanus. CCLXVII. 



