66 Miscellaneous. 



adduced before. It has been maintained that these animals are 

 varieties because no difference is to be found in their soft parts, 

 excepting as regards the general shape, which corresponds to that 

 of the shell. But I have observed, in Anodonta anntina, that the 

 branchial opening is not only comparatively, but actually, much 

 larger and fringed with much more delicate and numerous tenta- 

 cles than in Anodonta cygnea. 



There also seem to be conflicting ideas as to the direction in which 

 the respiratory current proceeds, some contending that it invari- 

 ably enters through the branchial orifice, and makes its exit through 

 the anal one, others that it may proceed either in this or the 

 reverse direction. I have taken some pains in investigating this 

 subject, and have repeatedly tried experiments with the animals to 

 find out the facts of the case ; and the conclusion I have arrived at 

 is, that, under ordinary circumstances, the current enters through 

 the branchial opening, and issues through the anal one only. It 

 may, however, in addition, enter at the anterior end or any inter- 

 mediate point; but it never issues from any place other than the 

 anal opening, excepting under peculiar circumstances, which I will 

 presently mention, and then it is spasmodically. The ordinary 

 position in which the animal is found is with the posterior end 

 projecting from the mud which forms the sides and bottom of its 

 habitat, the rest being imbedded in it. In this case, the direction 

 of the current is the normal one ; but should the animal choose to 

 repose wholly uncovered by the mud, as not unfrequently happens, 

 it then will separate the edges of the mantle from one another at 

 some point, and through this the water flows also into it. Should, 

 however, the branchial orifice from any cause become covered by 

 sand or mud and the anal one remain free, it Avill then draw water in 

 through the anal opening and expel it through the branchial one, 

 causing the sand or mud to bo blown away with very gi-eat violence, 

 after which the normal state of affairs is resumed. This action is 

 pixrely mechanical, the animal relaxing the adductor muscles, the 

 valves gape, the opening, however, which would otherwise have 

 been formed remaining closed by the thickened edges of the mantle 

 being kept in contact; this causes the water to enter the anal orifice; 

 then the valves are suddenly closed, and the water ejected through 

 the branchial opening, the whole action being, in fact, exactly that 

 of a pair of bellows. If both orifices are covered and there is 

 water between the valves, they are brought together, and the bran- 

 chial one freed, the anal one afterwards being uncovered by the 

 ordinary action of the current. Any other point on the free mar- 

 gin of the shell may be uncovered in a similar manner. These 

 facts I have tested by many trials, both with the Anodons and the 

 Unios. 



I remain, yours truly, 



R. M. Lloyd. 

 8 Weston Road, Handsworth, Birmingham, 

 Dec. 9th, 1869. 



