242 PISCES. 



their course. They consist partly of lacteals that proceed from the 

 intestinal canal, and partly of ordinary lymphatic vessels. When 

 filled by injection with quicksilver, they cover the vascular trunks, 

 the veins for instance, completely. They unite in the anterior part 

 of the body, and pour their contents by two trunks into the anterior, 

 and partly also by several branches into the posterior, venae cavae. 

 The main trunks (ductus thoracici) proceed from lymphatic sinuses 

 near the cardiac orifice of the stomach, analogous to the cisterna chyli. 

 Several lesser lymphatic branches would appear to lose themselves 

 in venous ramuscules. 



Peculiar Caudal and Cranial sinuses and a special system of Lat- 

 eral vessels were recently discovered in Fishes, and seem to belong to 

 the lymphatic system. Beneath what has been formerly described 

 (p. 185) as the lateral or mucous canal of the integument, we find 

 another sinus-like canal that is filled with a clear and limpid lymph, 

 and communicates with a number of adjacent branches, all pursuing 

 a subcutaneous course, and forming a ring of vessels around each 

 scale, so that the body of Fishes is completely intersected by this 

 net-work. This system of vessels communicates with a peculiar 

 caudal sinus, that is placed in many Fishes, as the Eel, in the same 

 situation as the caudal heart, which will presently be described. 

 This sinus is double, the divisions lying close upon either side of the 

 flat rays supporting the caudal fin ; but both of them communicate 

 by means of a transverse canal that passes through an opening in 

 one of the fin-rays. The sinus varies in size, and passes into the 

 caudal vein, being there providecL with a valve. It is invested by a 

 strong fibrous tunic, and contains a clear lymph ; whether it is en- 

 dowed with powers of expansion and contraction has not yet been 

 determined. A similar sinus has been observed upon either side the 

 cranial cavity external to the jugular veins ; it is pear-shaped, smaller 

 than the caudal sinus, and appears to be contractile. The occurrence 

 and position of these reservoirs remind us very much of the lymphatic 

 hearts of the Amphibia. 



The Blood of Fishes is, with one single exception, of a red color, 

 and contains almost always oval, flat, and slightly biconvex corpus- 

 cules ; those in the Plagiostomi are distinguished by their great size, , 

 and in this respect, as well as in their form, agree with those of 

 Frogs ; in the Osseous Fishes they are smaller. The Cyclostomi, at 

 least Petromyzon, have, however, circular biconcave corpuscules re- 

 sembling the human, but larger. 



The greatest departure from the circulatory system of the rest of 



