60 SUMMARY OF CURRENT RESEARCHES RELATING TO 



group ; they are open at the base of the ciliated grooves, and a few open in 

 the intercellnlar spaces of the roof of the duct, or a few unicellular glands 

 in the groove on the lateral margin of the foot. 



With regard to the calcareous cells of the liver, Dr. Brock remarks that 

 they were present in the earliest stages of development studied by him ; he 

 asserts, as against Leydig, that the foot is continuously ciliated, and he 

 draws attention to the little known fact that the right edge of the margin 

 of the mantle, in the region of the respiratory cleft, is also ciliated. 



Nervous System of Ctenobranch Molluscs.* — M. E. L. Bouvier finds 

 that the proboscidial commissure which is found in scutibranch proso- 

 branchiate Gastropods disappears from the ctenobranchiate group ; but 

 there is another connective which is very characteristic ; it is that which 

 more or less distinctly connects the right commissural ganglion with the 

 subintestinal. This connective results from the anastomosis of the right 

 pallial nerves which issue from the right commissural and from the sub- 

 intestinal ganglia. The author enumerates various forms in which this 

 arrangement is found. In the Cerithiidse the conversion of the anastomosis 

 into a connective may be studied step by step. When once formed, it 

 varies very greatly in dimensions. 



On the left-hand side the pallial nerve always retains its origin in 

 the commissural ganglion, except in Ampullaria, when it is converted 

 into a connective, going from the left commissural to the supra-intestinal 

 ganglion. 



Strength of Snails.f — Mr. E. Pandford has found that a snail weighing 

 1/4 oz. could drag up vertically a load of 2| oz. Another snail, 1/3 oz. in 

 weight, could carry horizontally a weight of 17 oz. 



Histological Peculiarities of Lamellibranchs.J — M. L. Eoule finds 

 that the blood-channels of Lamellibranchs do not (except in the heart and 

 pericardium) present the histological characters of closed vessels — that is, 

 proper muscular and connective-tissue walls which can be isolated from the 

 surrounding tissues. The canals are simple lacunae united into a difi'used 

 plexus, with the exception of a few which ordinarily communicate between 

 the heart and the organs. These last, which are generally known as 

 arteries, have not really a structure different from that of other lacunae. 

 Numerous muscular fibres do, indeed, surround their cavities, but they are 

 not proper to them. The connective layer which directly limits the cavity 

 does not differ from that which is situated more deeply, and does not form 

 a special membrane. Just like that of Tunicates, the whole circulatory 

 apparatus of Lamellibranchs 'recalls the lymphatic system of Vertebrates, 

 and the globules comjiletely answer to those of the lymph. 



A state of complete extension is habitual for the turgescent organs of 

 individuals placed under normal conditions of environment ; and contraction 

 is a temporary stage, followed by a return to the ordinary condition. In all 

 the turgescent organs the muscular bundles are numerous, and are set in 

 the direction of the retraction and extension of the organs. The siphons 

 and the edge of the mantle are not, any more than the foot, provided with 

 pores, which serve as organs of exit for the blood during contraction or 

 for the admission of water during extension. The mass of blood is of itself 

 sufficient to explain all the variations of volume, according as it is trans- 

 ported from one region to another. 



* Comptes Kendus, ciii. (1886) pp. 938-9. 



t Zoologist, X. (1886) p. 491. 



J Comptes Rendiis, ciii. (188G) pp. 936-8. 



