MORPHOLOGY OF THE AMPHINEURA. 223 



are separate in this subdivision of the Amphineura, appear to be 

 in close connection with each other in the Solenogastres. 



Our knowledge of the nephridia of Chiton has only very lately 

 been thoroughly estabhshed by Sedgwick (19). They are double, 

 and open into the pericardium at one end, into the palHal groove 

 between the branchise at the other. From the pericardium the 

 duct bends forwards towards the head, makes a very sharp turn 

 backwards again, enlarges to a kind of bladder, from whence a 

 short duct leads outwards at a very short distance behind the 

 exterior opening of the genital ducts. Numerous fine branches 

 and delicate ramifications (not represented in the woodcut) are 

 in direct commnnication with these ducts, and form the mass of 

 the renal organs.^ 



It needs no further inquiry whether the kidney, with a single> 

 posterior, median opening, such as it was described by v. Jhering 

 (10), is really to be found in any existing species of Chiton, as 

 Dr. Brock of Gottingen kindly writes to tell me that v. Jhering 

 has lately withdrawn this view as reposing on an erroneous ob- 

 servation, and has been convinced of the presence of lateral renal 

 openings (prior to Sedgwick's exhaustive researches). 



We have now to consider the other subdivision of the Amphi- 

 NEURA, the Solenogastres. A direct communication between 

 the ovary and the pericardium has been demonstrated in Fro- 

 neomenia (7) and Chatoderma (6). In Neomenia carinata its 

 presence is probable in the highest degree (32), although neither 

 here nor in Chatoderma have the ducts been separately made 

 out. 



In the second place the different genera of Solenogastres 

 are provided with a system of ducts and passages by which the 

 pericardium communicates with the exterior. These ducts, or 

 parts of them, are considered by the different authors on grounds 

 for which we refer to the original papers (6, 7) as renal organs. 

 There can be no serious doubt about their homology with those 

 of the Chitones. And so the Solenogastres exemplify a primi- 

 tive stage, in which the pericardium (body-cavity) receives the 

 oviducts, on the one hand, and on the other communicates with 

 the exterior by means of the nephridia. This latter communica- 

 tion persists in a very large number of Molluscs ; the former, 

 however, has been given up, but it is exceedingly instructive 

 and remarkable that (as a remnant of it) in the most primitive 

 genera of different classes of IViolluscs {Dentalium, Patella, Fis- 



1 I may here add that these recent observations of Sedgwick's have 

 been fully confirmed by Mr. J. F. van Bemmelen, who dissected a large 

 species of Chiton from the Indian Ocean, and showed me his preparations, 

 which I found to correspond in all important respects with Sedgwick's 

 account. 



