ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 551 



common enough. After an account of the difficulties which he per- 

 sonally suffered in trying to get these molluscs for dissection, and a 

 discussion of its general characters, the author describes the structure 

 of the shell, in which he distinguishes the true from the false shell. 

 The former, as is well known, consists of two small valves, and 

 possibly also of zones which extend beyond their limits ; the latter is 

 tubular in form, and presents differences in sections taken at different 

 points. In the terminal or lower part the calcareous tissue is pretty 

 compact, and is formed of a number of layers which can be easily 

 separated from one another, and do, as a fact, so easily part that it is 

 impossible to make a satisfactory circular section of the tube. The 

 facts of structure seem to show that the secretion of the false shell and 

 its mode of growth depend on a deposit of crystalline particles, which, 

 when effected slowly, gives rise to spheres, and when rapidly, to 

 needle-shaped bodies. With regard to the marks or lines of attach- 

 ment of the muscles, which are so prominent a feature in the shells of 

 ordinary Lamellibranchs, it is here difficult to speak with certainty, 

 and such lines of insertion as can be made out are hard to describe, 

 inasmuch as they vary in depth in different individuals, and have not 

 always exactly the same contour. 



To examine the animal that forms the shell it is necessary to break 

 the latter, for it is impossible to extract by the lower orifice a conical 

 body, in which the base has, of course, a longer diameter than its 

 truncated apex. The body has a chitinous envelope which is probably, 

 though not quite certainly, secreted by the mantle ; this last has no 

 remarkable characteristics. The description of the mantle is followed 

 by a general account of the structure of the animal, and the author 

 then passes to the digestive tube. 



The dissection of the digestive tube was long and laborious on 

 account of the intimate relations of the genital and hepatic glands ; 

 as in other Lamellibranchs it describes a convoluted or appa- 

 rently capricious courge. The form of the anus is remarkable in 

 consequence of its being affected by a constriction quite close to the 

 end of the rectum ; the extremity has the form of a small spherule, 

 and the orifice is bilabiate. Within the interior of the intestine there 

 is a projection comparable to the typhlosole of the earthworm ; in the 

 stomach the same ingrowth has a number of folds. No csecum or 

 hyaline style was to be observed. The oesophagus is certainly much 

 longer in Aspergillum than in any other Lamellibranch ; the mouth is 

 very easy to find, and appears to have a definite relation to the superior 

 orifice of the disk of the mantle. The liver, as in all its allies, is well 

 developed ; though the condition of his specimens did not enable the 

 author to make altogether satisfactory preparations, he thinks that it 

 agrees in essential characters with that of other Lamellibranchs. 



The organ of Bojanus is heart-shaped in form and brownish in 

 colour ; the pericardiac orifices are relatively easy to find, and, as in 

 Anorhm, the external orifices are situated at a high level. It is, 

 without doubt, the organ that was described by Euppcll as the 

 liver. 



The central organs of circulation closely resemble those of other 



