250 Dr. T. Williams on the Mechanism of Aquatic 



in the urine of the Vertebrated animal, are not necessarily to be 

 regarded as the basis and essence of the analogous secretion of 

 the lowest Invertebrata. If such reasoning were grounded on 

 truth, it would involve a ridiculous paradox to deny that the 

 minute anatomy of this system of glands was not precisely the 

 same in every grade of the series. But it may be proved im- 

 mediately, and most readily, that the Malpighian coils of capil- 

 laries, so constantly and essentially distinctive of the kidney 

 even of the lowest Vertebrated animal, disappear in toto from 

 that of the Gasteropods and the Cephalopod. Here, at the very 

 first step, the fundamental structural element of the higher 

 phase of the organ vanishes. If it be so, is it not reasonable to 

 infer that a correspondingly marked and essential change has 

 occurred in the secreted product of each organ ? 



The preceding observations, general though they may be, are 

 abundantly sufficient to justify the assertion, that in the present 

 state of knowledge with reference to the comparative histology 

 of the renal system, and the comparative chemistry of the renal 

 secretion, the physiologist is not in a position to state with 

 certainty and confidence whether the alleged kidneys even of 

 the higher cephalous MoUusca are really so or not*. 



As the complete history of the glandular bodies which are 

 lodged in the respiratory cavity of the cephalous Mollusca will 

 rightly fall within the compass of another series of researches, 

 the author on this occasion will give only a slight sketch of their 

 structure, and that more because they are constant attendants 

 on the respiratory organs in this class of animals, and occupants 

 of the chamber dedicated to respiration, than because they are 

 asserted by some anatomists to be muciparous glands, and by 

 others no less distinguished as true kidneys. 



That gland (PI. XI. fig. 1 c', c', and fig. 3 g) which Cuvier 

 first designated "Forgane de la mucosite,'^ is unquestionably 

 traceable as one and the same body throughout various changes 



* During my recent studies among the Invertebrata, I have accumulated 

 a large mass of materials elucidatory of the serial anatomy of tlie renal 

 system. It would be quite irrelevant to enter further into details in this 

 place and upon this occasion. I trust that for such a task another oppor- 

 tunity will occur. I am deeply impressed with the belief that real service 

 will be rendered to the comparative anatomy of the Invertebrata even by 

 the publication of such results as have already been attained. It is certain 

 that the urea and uric acid tests, in determining the renal or non-renal 

 character of supposed kidneys in the case of the lower and lowest Inverte- 

 brata, lead to conclusions utterly unworthy of confidence. This point I 

 have abundantly proved. The presence of uric acid in the renal secretion 

 supposes a highly nitrogenous or proteinized composition of the blood, — in 

 fact, such complex conditions as do not exist in the fluids of the lower 

 invertebrated animal. 



