266 On the A-ffinities of the Oncliidia. 



Ntisslin* in various Pulmonata. The absence of this organ 

 in Onchiclmm^ asserted by Joyeux-LafFuie and Brock, is also 

 incorrect, seeing that I have ascertained its existence in 0. 

 twnidum, Semp.t- The very fine aperture in the pericardium 

 occurs beneath the bottom of the auricle, a little to the left 

 side. At the hindmost part of the upper wall of the pulmo- 

 nary cavity there is the fine renal pore; it leads into a urine- 

 chamber^ at first narrow and afterwards wider, which extends, 

 rather superficially, through the whole length of the kidney, 

 bending with that organ. The lung is therefore not a dilated 

 terminal section of the kidney ^ and this the more because the 

 structure of the kidney and that of the wall of the lung are 

 quite different. 



The relationship of the Onchidia to the Pulmonata appears 

 with special distinctness in the structure of the generative 

 system. What strikes one here above all is the position of 

 the seminal duct in the lateral wall of the body. A similar 

 condition occurs in no Nudibranch, and has indeed only been 

 demonstrated in the Pulmonata. In the VeroJiicelloi ( Vagi- 

 nuke) the position of the seminal duct is the same, only the 

 portion of the duct enclosed in the musculature of the body is 

 shorter, because here the vulva is removed more forwards to 

 the middle of the length of the body. In the Auriculacete 

 and Lymnsese the same anatomical relation again makes its 

 appearance, but the enclosed portion of the duct has become 

 still shorter. Ihering's attempt:): to homologize the ciliated 

 groove of the Onchidia with that of the Steganobranchiata, 

 and to interpret the seminal duct of the former as only a vessel 

 constricted off from the bottom of the ciliated groove, is hardly 

 a very happy one. 



Consequently, then, the Onchidia agree with the Pulmonata 

 in the structure of the nervous system^ in the existence of a 

 lu7ig and of a parenchymatous hidney, in the presence of the 

 peculiar j)edal gland, and in various peculiarities of the 

 generative system. From a tolerably extensive knowledge of 

 the so-called Nudibranchs I cannot but regard the Onchidia as 

 pretty widely separated from them. On the contrary they 

 branch off from the Pulmonata ; they are Pidmonata which 

 have adapted themselves to an amphibiotic or marine mode of 

 life. 



* O. Niisslin, " Beitrage zur Anatomie und Physiologie der Pulmo- 

 naten," 1879, pp. 14, 15, iig. 3. 



+ R. Bergli, ' Challeiiger ' Expedition, I. c. p. 137, note 2. 



X H. von Ihering, ' Ueber die systematische Stellung von Peronia/ 

 1877, p. 29. 



