282 



PHYSIOLOGY OF THE INVERTEBRATA. 



The nutritive fluid (blood) of an edible crab weigting 

 . about 8000 grains contained : — 



Calcium phosphate . 

 Phosphoric acid 



11.10 grams 

 15-78 „ 



Having alluded to the secretion of the shells and exo- 

 skeletons in the Mollusca and Crustacea, we now proceed to 

 describe the organ of Bojanus in ATwdonta cygnea and other 

 Lamellibranchiata. The function of this organ has been 

 investigated by Mr. Harold Follows, F.O.S., and the author.* 

 It is a paired, elongated, oval, glandular sac with folded walls. 

 It is situated beneath and behind the pericardium, and in 

 front of the posterior adductor muscle (see Fig. 18). This 

 organ is composed of a yellowish or brownish spongy tissue, 

 which is covered with a closely ciliated, cellular layer. Its 

 secretion is acid to litmus paper, and it contains uric acid, 

 urea, and calcium phosphate. . The presence of these com- 

 pounds were proved by the methods already described in 

 this chapter. 



« CJiemical News, vol. 5 1, p. 241 ; Journal of Chemical Society, 1885, p- 9^' i 

 Proceedings of Boyal Society of Edinhurgh, vol. 14, p. 233. 



