90 CURRENT LITERATURE. 



Generative apparatus particularly simple; peculiar absence of accessory glands. 

 Spermatozoa and ova in separate follicles of hermaphrodite glands. Penis 

 invaginable, grooved. 



Heart obliquely situated on left side of floor of mantle-cavity : ventricle 

 posterior, sinistral ; auricle anterior, dextral. This disposition of heart's axis 

 closely approaches that of Prosobranchia. Auricle receives two branchial veins 

 (cf. Umbrella, in which Haller cites Moquin-Tandon as to existence of a posterior 

 vein also, but degenerate). 



Gills in form of a U-shaped series of plumes along posterior border of mantle- 

 cavity, decreasing in size from right to left, and bounded internally by a venous 

 channel, externally by an arterial channel. There is a group of particularly large 

 plumes on right side anteriorly, separated from remainder by a transverse blood- 

 vessel, which connects venous lacuna; of right nephridium with branchial artery. 



Haller regards each gill-plume as a true ctenidium. He derives the Opistho- 

 branchia from the Prosobranch stem, at a stage when the ctenidia, nephridia and 

 auricles were still paired. The ctenidia then became serially repeated down each 

 side of the body (cf. Chiton, where the multiplication of ctenidia is also correlated 

 with the duplication of the branchial veins). Subsequently the entire left row of 

 ctenidia, together with the left auricle, was lost ; and Siphonaria is regarded, as 

 representing this stage, slightly modified in adaptation to the conditions of rock- 

 existence. The Umb re I la -stage is reached by degeneration of the posterior part of 

 the complete ctenidial series, the so-called gill-plume of the Pleurobranchia being 

 represented in Siphonaria by merely the right anterior group of large ctenidia. 

 Correlated with this degeneration, the composite gill-plume of the Pleurobranchia 

 is regarded as having migrated backwards (cf. position of anus), thus causing 

 a corresponding rotation of the heart's axis, until the auricle came to lie behind 

 the ventricle once more. 



A special group of Tectibranchia — the Semicyclobranchia — is proposed for the 

 reception of Siphonaria and any other forms that may be found to possess the 

 complete right-sided series of ctenidia. 



We may point out two objections to this ingenious theory in its present form. 

 Firstly, we fail to verify Haller's reference to Moquin-Tandon's " Recherches sur 

 1'Ombrelle " in regard to the existence of a rudimentary posterior branchial vein 

 behind the gill-plume in that form. An anterior and a posterior vein are 

 certainly mentioned ; but they are equally functional, and convey the arterialised 

 blood to the auricle from the anterior and posterior parts of the functional gill- 

 plume respectively. Now much of Haller's reasoning depends upon the supposed 

 existence of this rudimentary vein. 



Secondly, if the mantle-cavity of Siphonaria is compared with the sub-pallial 

 furrow of Umbrella, it may readily be seen that the position of the " ctenidia" in 

 the former is diametrically opposed to several of Haller's contentions. The small 

 posterior "ctenidia" on the left side in Siphonaria can only represent the most 

 anterior ctenidia in Umbrella ; for the gradual reduction of the branchial or 

 pallial invagination in Siphonaria would result in the straightening out of the horse- 

 shoe-shaped row of " ctenidia " nntil the apex of the lelt limb became anterior, 

 and the apex of the right limb posterior in position. The mode of attachment 

 of the large " ctenidia " in Siphonaria points equally to the same conclusion. 



We commend these points to Haller's re-consideration. — W. G. 

 The Liver of Gasteropods. (Pull. Sci. de la Fiance, etc., xxiv, 87 pp., 

 pts. i-6, 1892.) 



Mons. H. Fischer's paper is of great interest. The various stages of develop- 

 ment are dealt with at some length. The principal variations are noted, e.g., the 

 symmetry of the hepatic lobes, the number of hepatic canals, &C. Although this 

 organ can be traced from a comparative primitive condition to a somewhat 

 complex one, M. Fischer does not think the general modifications which can be 

 established, are sufficiently important to base generic, &c, distinctions upon. 



Limax maximus v. cinereo-niger.Wolf. (Ann. and Mag. N.H., p. 425, 1892.) 

 Mr. Walter E. Collinge, who has lately examined British examples of this 

 variety, confirms the remarks of Simroth and Scharff, viz., that it is but a colour 

 variation of L. maximus, L. , and that there are no anatomical differences in the 

 two forms of sufficient importance to raise it to specific rank. 



