794 SUMMARY or CUERENT RESEARCHES RELATING TO 



vascular apparatus are very constant ; tlie right commissural ganglion 

 gives off but one nerve, and this passes to the side walls of the body. 

 There are not many important differences between Nassa and Buc- 

 cinum ; in the Purpuridse the proboscis is much shorter than in the 

 whelk, the cerebral ganglia are closely united. Concholepas is dis- 

 tinguished from Purpura by a number of characters ; it is apparently 

 a Purpura modified by adaptation ; the posterior lobe of the foot 

 being atrophied and the anterior enormously developed, the viscera 

 have come to lie on the back. 



Communication of the Vascular System with the Exterior in 

 Pleurobranchus.* — Dr. A. G. Bourne, referring to the description by 

 Lacaze-Duthiers of a special canal, opening on the one hand to the 

 exterior and on the other to the branchial vein in Pleurobranchus, 

 denies its existence. The orifice leads into a sac which is entirely 

 closed ; the sac itself is lined by epithelium v^^hich dips down into 

 branched crypts, and is of very different thicknesses in different 

 regions; in the more thickened parts there are glandular contents 

 which stain deeply. By the use of injection methods it would have 

 been easy to rupture the thin membrane which divides the lumen of 

 the sac from that of the branchial vein. If this sac is nephridial in 

 nature it is the rudiment of the second nephridium which persists in 

 S3 few Gastropods (e. g. Fissurella, Patella) ; this does not seem to be 

 probable, and it is more likely that, as Prof. Lankester has suggested, 

 it is the homologue of the grape- shaped structure in Aplysia which 

 has long been known as the " poison-gland." 



Inception of Water among MoUusca.t — Dr. H. Griesbach con- 

 tributes some further remarks upon this vexed question ; they 

 consist mainly of a criticism of Lankester's results, who disbelieves 

 any such inception on account of (1) the presence of hgemoglobin in 

 the blood of Planorhis and Solen, (2) the impossibility of discovering 

 apertures in the foot communicating with the blood-channels. Nalepa 

 has however proved that the subepithelial blood-vessels do com- 

 municate with the exterior by pores ; and this observation has been 

 confirmed by Schiemenz. Lankester has denied the shedding-out of 

 water by the kidney because the pericardium is not a vascular space. 

 Griesbach, on the other hand, asserts that it is, and that it can be 

 proved to be so by careful injections. 



Relations of Cavernous Spaces in the Connective Tissue of 

 Anodonta to the Blood-vascular System.J — Dr. P. Scliiiler has come 

 to the same conclusions from a study of Anodonta as did Flemming with 

 Mytilus ; and he likewise objects to Griesbach 's method of " Selbst- 

 injectionen." He has no doubt that the cavities in the mantle and 

 foot of Anodonta are cells with clear mucoid contents. If we had to 

 do with wall-less blood-lacunse it would not be possible to isolate the 

 vesicles ; the injected preparations show conclusively that the vesicles 

 are cells and that the vascular system is closed. The vessels which 



* Quart. Journ. Micr. Sci., xsv. (1885) pp. 429-31 (1 pi.). 



t Zoo]. Anzeig., viii. (1885) pp. 329-32. 



X Arch. f. Mikr. Anai, xxv. (1885) pp. 84-8. 



