246 Zoological Collections. Invertebrata. 



It is not our intention now to enter into a particular description of the 

 organs in the Arenicola, to which we have alluded. Suffice it to say, as our 

 object is merely to direct attention to the fact at this season of the year so 

 favourable for investigations of this nature, that, attached to the concave sur- 

 face of the sacs, or livers of Home, which are disposed on each side of the 

 anterior third of the body, (see Home, Comp. Anat. vol. iv, tab. xl,) is 

 a vascular membrane, around the fimbriated margins, and over the surface 

 of which, rapid motions are seen to be produced by vibrating cilice, (if that 

 term be applicable to certain peculiarities observable in the structure of these 

 organs.) The communication of the vessels is easily traced to the principal 

 vascular trunks. 



These motions appear to us to be entirely unconnected with the respira- 

 tory process ; but we must reserve to ourselves the development of our 

 views till a more convenient occasion. * If it should, however, be supposed 

 that these sacs may possibly be a second system of branchiae, analogous 

 to the respiratory vesicles of the leech, we would remark, that the ciliary 

 motions in the interior of the animal can have no influence in moving water 

 contained within the sacs ; and we may farther mention, that, although 

 there is a peculiar canal stretching along the surfaces of each articular 

 segment leading from the middle line to an external orifice, (but apparently 

 not opening internally,) we could observe no aperture leading to the sacs. 



We may here mention, that in the terminal extremities of the coeca of the 

 sea-mouse, {Halithcea aculeata,) contained within sacs under the dorsal plates, 

 we have also seen similar motions, though very faint in degree ; and Dr 

 Sharpey informs us tiu;; he also has observed them. It is the opinion of 

 Carus and Treviranus, that the intestinal canal here takes on the function 

 of respiration ; in which case these may be considered as true respiratory 

 motions ; but there are difficulties with respect to that opinion. The 

 motions, however, in the HalithcEa are not to be confounded with those 

 above noticed in the Arenicola. "We shall return to this subject — Eo. 



j ■ Anatomical Observations on the Cyclades ; by L. L. Jacobson. — Wishing to 

 determine if the young of the bivalves, from the commencement of their 

 development, resemble their mothers, or if they undergo any metamorphosis, 

 M. Jacobson has conducted a series of observations upon the Ostrea, Mytilus, 

 Cardium, and Mya, but without success. He has, however, been more 

 fortunate in examining a little fresh water species, the Cyclas cornea, which 

 is frequently found in the canals of Denmark. The animal is small in pro- 

 portion to the shell ; on opening which, however, he discovered the foot placed 

 in the middle, the organs of respiration, and the cellular tissue contained 

 between the pellicles which attach the animal to the shell. The foot, as is 

 well known, is the organ which serves for locomotion ; this species can 

 elongate it more than any other animals ; strong ligaments attach it to the 

 belly. In the belly the apparatus of digestion is immediately perceptible. 

 The mouth is round, and surrounded by four tentacula, which are of a 

 triangular and pointed form ; the stomach is encircled by the liver ; the 

 intestinal canal descends directly towards the ovary, reascends towards the 

 back, forms an angle there, and redescends towards the heart to terminate 

 at the anus. The lower part of this canal is frequently filled with a mass 

 of a deep greenish colour. 



differs from the true Amphitrite, in having what were supposed to be the branchiae much 

 shorter, and never advanced, whilst the latter has them of very large size, and susceptible 

 of considerable motion. 



* Dr Sharpey is of opinion, that " in the bivalve mollusca, the property of exciting- 

 motions in the water may serve other important purposes besides respiration, and it is 

 probably in this way," he remarks, ♦' that their nutriment is carried to the mouth, and 

 that the ova are excreted, or conveyed from one part of the body to another." We con- 

 ceive that, in the case above alluded to, these motions will be found to serve very different 

 and far higher functions than those here mentioned. 



