102 Miscellaneous. 



It was in the month of October 1870 that, for the first time, I 

 chanced to meet with Oncidium celticum on the walls of the Brian- 

 tais, towards the embouchure of the Ranee ; I could not aftei'wards 

 find it during the winter months ; and it was only in March 1871 

 that I saw a few individuals reappear. It is therefore probable 

 that, like many other pulmonate Gasteropods, this animal does not 

 come out during the cold season. After this period I at first found 

 some difficulty in procui-ing it, in consequence of my not having 

 studied with sufficient care the circumstances under which it is to be 

 met with. In fact this mollusk only inhabits a very restricted zone, 

 corresponding pretty exactly to the upper part of the second zone of 

 MM. Audouin and Milne-Edwards, characterized by the presence of 

 Fucodium nodosum ; nor does it exist at all parts of this ; and it 

 appears especially to seek the spots covered with that greyish mud 

 which is known by the name of tangue, and, I believe, where infil- 

 trations of fresh water may be met with ; this last fact, which is 

 always difficult to ascertain, requires confirmation. Lastly, these 

 animals do not at all times issue from the fissures which they 

 inhabit ; it is when the level just mentioned has been uncovered 

 for about an hour that they begin to appear in numbers : for about 

 two hours we may see them crawling to and fro upon the mud ; 

 afterwards they become scarce and disappear. In mild and bright 

 weather they are more numerous ; nevertheless I have likewise 

 found them in the rain ; they have therefore much less dread of 

 fresh water than a great number of other marine animals. 



The nervous and digestive apparatus, although presenting inter- 

 esting pecuHarities, have been described with so much care, at least 

 in fundamental points, that I do not think I need speak of them 

 here. 



The arterial system is remarkable in most individxials by its 

 peculiar aspect ; the vessels of which it consists, and their ramifi- 

 cations, are of a silvery whiteness, resembling, in a certain degree, 

 the tracheae of insects ; but here this eff'ect is due to the accumulation 

 in the walls of refractive, fatty granulations. This colour is more or 

 less marked, and depends, perhaps, ui^on the season or the state of 

 the individual ; this question I was unable to decide. The prin- 

 cipal trunks are three in number : — one anterior, neuromuscular ; a 

 second, middle one, gastro-hepatic ; the last genital. The blood 

 returns to the heart, at least in great part, by venous vessels, situ- 

 ated in the dorso-lateral walls, vessels which open into two great 

 lateral sinuses (veins of Cuvier) ; and these sinuses themselves enter 

 the pulmonary vessels. 



Respiration, as is shown by anatomy and by observation, is per- 

 formed in two ways-^namely, by the so-called loidmonary cavity 

 and by the skin. In the first place the dorso-lateral veins, which I 

 have just mentioned, evidently collect hsematosed blood from the 

 cutaneous surface; their arrangement sufficiently indicates this. 

 On another hand, if we place one of these animals in sea-water and 

 keep it there, contrary to what has been stated by some authors, it 

 lives there perfectly well, although it can respire only by the skin. 

 Moreover, by examining the way in which the animal behaves in 



