BLOOD OF REPTILES. 501 



In these the size is greater in the ratio of the persistence of the 

 branchial apparatus ; and the perennibranchiates present the 

 biggest blood-discs absolutely,, as well as in proportion to the size 

 of the body, of all vertebrate animals. The two extremes in the 

 relative size of the blood-discs in piilmonated Hcematocrya are 

 shown in those of a Crocodile, which was twenty feet in length, 

 p. 4, fig. 8, e, and in those of a Siren lacertina, which was two 

 feet in length, ib. f. The latter, which are just visible to the 

 naked eye, serve to demonstrate the highly refractive divisions of 

 the nucleus, and the nuclear capsule. 1 



There is less blood in cold-blooded than in warm-blooded 

 animals, and more blood in some fishes, the Tunny, e. g., than in 

 any reptile. Dr. Joseph Jones 2 estimates the average quantity 

 of blood to be : 



In Serpents . . . ^ to ^ of the weight of the body. 



Emys terrapin ^ to ^ 



Emys serrata . . ^ to ^ ,, 



Testudo polyphemus TI^ TT 



Blood drawn from a living Batrachian is of a purplish red 

 colour, and coagulates into a clot including the discs, floating in 

 clear serum. The clot is firmer than that of fishes, but less firm 

 than in allantoic reptiles ; in a few hours the clot dissolves and 

 liberates the discs. In the recently drawn blood of Chelonia 

 most of the discs settle at the bottom of the vessel, and are not 

 included in the clear clot which forms above them. The fibrin in 

 this clot speedily passes into albumen. The colour of the serum 

 in most reptiles, e. g. Batrachia, Ophidia, Crocodilia, and some 

 Chelonia ( Testudo polyphemus), is a light yellow : in many carni- 

 vorous Chelonia (Emys serrata, E. reticulata, E. terrapin), it is of 

 a golden colour. When treated with a drop of sulphuric acid, 

 and gently heated, the peculiar smell of the species, due, e. g. in 

 the Alligator, to the musk-glands, and in the Rattlesnake to the 

 anal glands, is plainly developed. 



The blood of Ophidia contains the greatest proportion of solid 

 constituents, in the cold-blooded Vertebrates. 3 



88. Veins of Reptiles.- -The capillary blood-vessels having a 

 calibre proportionate to the diameter of the blood-discs which 

 flow along them in single file, are largest in the Batrachia, in 

 which class the best examples are afforded for demonstrating to 



1 CCLXXIII. and CCLXXIV. 2 CCXLV. 



3 Dr. Joseph Jones, from whose excellent and original work (CCXLV.) most of the 

 above particulars are taken, suggests that the richness of the ophidian blood may be 

 due to the fact of serpents seldom, if ever, drinking. The comparatively unimportant 

 details of the diameters of reptilian blood-discs may be seen in ccxxxix, tome i 

 p. 89. 



