368 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of sections ; by these means it was ascertained that the reno-pericardial 

 opening was continuous with a canal running back through the sub- 

 stance of the kidney and opening below into its cavity. The external 

 aperture of the kidney is situated below the line of attachment of the 

 gill wliich traverses the surface of the organ, and close to its posterior 

 extremity. In structure the kidney consists of a number of trabeculse 

 forming a network ; in the interior of the trabeculse are numerous 

 blood lacunae which are sometimes traversed by delicate strands of 

 connective tissue ; on either side of the trabeculse are the renal cells, 

 none of which appear to be ciliated. The kidney of Aplysia cor- 

 responds morphologically to the left kidney of Zeugobranchia and 

 Patella. 



Visual Organs of Lamellibranchs.* — B. Sharp has examined the 

 edge of the mantle of Ostrea virginica and Mitilis edulis of the 

 Asiphonata, and the siphons of Venus mercenaria, Mya arenaria, 

 Mactra solidissima, besides the forms already described for Solen ensis 

 and S. vagina.'t The pigmented cells found in these parts are essen- 

 tially the same as those found in Solen ensis and S. vagina. The 

 smallest of all the cells were found in Ostrea, and the largest in 

 Venus. Experiments on these forms show their sensitiveness to 

 light and shadow, and the cells showing the retinal character described 

 leave little doubt as to the power of vision. No nerves could be 

 demonstrated passing direct to these cells, and probably those distri- 

 buted to the general epidermis serve in transmitting the impressions. 

 The visual power is so low, that nerves have not been yet specialized 

 for this purpose. 



MoUuscoida. 



Development of Salpa. j — In the second part of his researches into 

 the development of Salpce, Prof. W. Salensky deals with four species, 

 viz. S. punctata, S. fusiformis, S. hicaudata, and S. democratica ; 

 the differences observed between the species are very considerable, 

 and a general resume is given at the close of the memoir of the 

 differences in all the species studied. The ovum is contained in a fol- 

 licle which is a diverticulum of the respiratory chamber and connected 

 with it by a canal, the so-called oviduct ; in S. pinnata and others, this 

 cavity disappears in time, but in S. hicaudata it persists as a brood 

 pouch ; the " oviduct " opens upon the summit of a fold of the walls of 

 the respiratory cavity ; in some species (e. g. S. pinnata, S. africana) 

 another fold of the respiratory cavity of the mother rises round the 

 aperture of the oviduct ; these are termed Salpce tJiecogonce ; in others 

 again there is no such fold, and this group may be termed Salpce 

 gymnogonoe ; corresponding to this difference are other differences 

 both in the structure of the embryo and the development of its several 

 organs. 



In the first group the fold which immediately surrounds the 



* Proc. Acad. Nat. Sci. Philad., 1884, p. 10. This is the same article which 

 was given in brief abstract, ante, p. 213. 

 t See this Journal, ante, p. 39. 

 X MT. Zool. Stat. Neapel, iv. (1883) pp. 327-402 (6 pis.). 



