LYMPHATIC SYSTEM. 155 



Secondly, these vessels in fish either have no valves, or the 

 valves readily give way, for it is an easy matter to fill them 

 contrary to the- course of the lymph. When I first observed 

 this circumstance, I imagined that by injecting minutely those 

 vessels, I might discover their very beginnings, and that I might 

 also be enabled to determine whether such parts as the brain, 

 eye, &c., of which the lymphatics have not been yet seen in any 

 animal, have or have not such vessels. What success I have 

 had in these experiments will be related in a future publica- 

 tion (LXVII). 



Thirdly, the lacteals in the cod (and I presume in most 

 other fish) are remarkable for having a beautiful network of 

 vessels between the muscular and villous coat of the intestines. 1 

 This network may be filled from the lacteals on the mesentery 

 with the least force imaginable. If mercury be injected into 

 this network at one part, it spreads over the intestine, the 

 communications in the network being very numerous ; if the 

 intestine b'e inverted, and the mercury squeezed, it is easily 

 driven into the small vessels of the villi of the internal coat. 2 

 From these vessels the mercury can be forced into the cavity 

 of the intestine ; but not so easily as to make it clear whether 

 they have or have not a valve at their beginning. In these 

 circumstances there is a strong analogy between fish and the 

 turtle ; but in fish it is more evident that there can be no de- 

 ception as to the network between the muscular and the in- 

 ternal coat ; for in them it is made up of cylindrical vessels, 

 and is not cellular as in the turtle, and therefore not in the 

 least like an extravasation ; and in fish the vessels on the in- 

 ternal coat are larger than in the turtle. 



Fourthly, this system agrees with that of the turtle, in hav- 

 ing a very large receptaculum, and in having the network of 

 large vessels near its termination in the sanguiferous system ; 



1 I have seen this network in the turbot, plaice, and cod. 



2 If instead of mercury a thin size be used, as an injection it will run with the 

 same facility into the lacteals upon the villi, as it would do into their arteries and 

 veins, when thrown in by a pipe fixed in those vessels. 



(LXVII.) Mr. Hewson died May 1, 1774, the same year that this 

 second part of his Experimental Inquiries was published. Dr. James 

 Heudy a mentions Mr. Falconar's supposition, that he had injected 

 lymphatic vessels in the brain of the cod-fish. 



a On Glandular Secretion, p. 7, 8vo, Lond. 1775. 



