428 PEOFESSOR E. RAY LANKESTER. 



original space representing them both in the ancestors of these 

 two great phyla. The author stated that he had been led to 

 the view which he now formulated by his discovery of distinct 

 spaces in both Mollusca and Arthropoda, which appear to be 

 the true coelom, and are separate from the swollen vascular 

 system. 



'' In Mollusca the pericardial space is the chief representa- 

 tive of coelom. It is usually taught that the pericardium of 

 Molluscs contains blood, and is in free communication with 

 veins ; but the author had succeeded in showing by observa- 

 tions on the red-blooded Solen leg u men (already published, 

 ' Zoolog. Anzeiger/ No. 170, 1884), and by more recent 

 careful investigation of Anodonta cygnea, Patella vul- 

 gata, and Helix aspersa, that the pericardium has no 

 communication with the vascular system, and does not contain 

 blood. The perigonadial spaces (so-called generative glands) 

 and the pericardial space (which has arborescent tubular out- 

 growths in some Lamellibranchs forming Keber's organ) are, 

 then, the coelom of the Mollusca. It is quite distinct from the 

 hsemocoel. In Cephalopods, and in the archaic Gastropod 

 Neomenia, the pericardial and perigonadial coelomic remnants 

 are continuous, and form one cavity. There is strong reason 

 to believe that in ancestral Molluscs the hsemoccel was more 

 completely tubular and truly vasiform than it is in living 

 Molluscs. In the later Molluscs the walls of the vessels have 

 swollen out in many regions (especially the veins), and have 

 obliterated the coelom, which has shrunk to the small dimen- 

 sions of pericardium and perigonadium. There are, however, 

 many Molluscs with complete capillaries, arteries, and veins, 

 in certain regions of the body. These had been recently 

 studied by the author by means of injections, and by silver 

 impregnation, and drawings illustrative of them were exhibited 

 to the Section. 



" With regard to the Arthropoda, Professor Lankester formu- 

 lated the same view, viz. that the ancestral blood-vessels have 

 swollen and enlarged, especially the veins, so as to form large 

 irregular spaces, which have blocked up and so obliterated the 



