Miscellaneous. 367 



but of sinuses with proper walls. However, all the German zoolo- 

 gists appear to have passed into the camp of M. Milne-Edwards. 

 M. Eberth alone, in consequence of some injections with nitrate 

 of silver, thinks he has ascertained that the blood-canals of the 

 Gasteropoda have proper walls, and cannot be regarded as lacuna?. 



The best method of studpng the circulatorj' passages of the Gas- 

 teropoda is to make an injection by the ventricle, or, still better, by 

 the auricle or by a large vessel. There are, however, some cases in 

 which this method cannot be employed — as, for example, among the 

 Mur'ues and the Turbines, in which the heart, which is extremely 

 small, is protected by the thickest part of the shell. In these cases 

 M.Wedl has also employed the method of pricking in the neighbour- 

 hood of the sinuses or of some large vessel. 



The result of the numerous researches of M. Wedl is to prove the 

 existence in the Mollusca of a completely closed vascular system, 

 with capillary networks in the greater part, of the organs. The 

 type of distribution of these is extremely variable, and intimately 

 connected with the structure. It is thus that in the 3Iti rices the 

 skin of the trunk and of the back is formed of several superposed 

 layers of muscular fibres, crossed in different directions, and that 

 several networks of l)lood-vessels are likewise superposed in these 

 parts. The vascular networks are superposed in the same manner 

 in the foot of these Ctenobranchs. In the warty skin of Helix we 

 find a distinct capillary system for each verrucosity. In all cases 

 where the skin is very erectile, as in the foot of the Limaces, the 

 capillary vessels are very large, and embrace very small meshes. 

 The very erectile part of the mantle presents an extraordinary vas- 

 cularity with very narrow meshes, whilst that part of the mantle 

 which envelopes the kidneys and the liver does not present by any 

 means a like richness. In no part of the skin is there any commu- 

 nication between the veins and the exterior. Nor do the veins 

 appear to communicate with the aquiferous vessels. M.Wedl, liow- 

 ever, has not been able to determine whether these last open directly 

 into the perivisceral cavity, or whether they are distributed only in 

 the foot. 



The digestive organs of the Gasteropoda present great variations 

 in their intimate structure. Among the Helices and Limaces, the 

 circulatory system both of the mucous and of the external surface 

 of the intestine is perfectly closed. There even exists a rich capil- 

 lary network in the duplicature of the mucous membrane which 

 encloses the radula. In the liver, which has no portal system, the 

 bile is secreted by the arterial blood. Some arteries encompass the 

 acini ; the mode of ramification of the vessels is that of a clustered 

 gland. 



The capillary network of the inner surface of the lungs in the 

 pulmonate Mollusca is one of the richest in the organism, just like 

 that of the branchia) in the Ctenobranchs. We find networks com- 

 posed of large meshes in the kidneys, around the mucus-glands and 

 flageUum, and in the seminal capsule (in Heli.r), whilst the albumi- 



