834 TEOF. G. C. BOURXE OX THE [Nov. 17, 



cavities, are so similar in Septaria to those described by Lenssen in 

 JVeritiua fluviaiilis, that it is not necessary to enter into any 

 further description of them. 



TJie Hcemoccele and Ccelom. 



The cavities in which lie the buccal bulb, the oesophagus, 

 radvila-sac, and the coils of the intestine are, as is usually the case 

 in Molluscs, a vast blood-space or lijemoccele. In most Neritidse 

 and in the Helicinidse this space is largely filled np by a parenchy- 

 matous tissue, which from its structure and position appears to 

 be metabolic in function and probably serves for the storage of 

 reserve material. Whei-e present it is aggregated along the courses 

 of the chief arterial vessels, and a certain ainount of it is to be 

 found surrounding the anterior aorta in Septaria. This metabolic 

 tissue, however, is never abundant in Septaria, and I postpone 

 a description of it to the section dealing with the Xeritce and 

 Neritince. In Septaria, and indeed in all iNTeritidse, the large 

 hffimocoelic cavity does not extend as a wide space into the visceral 

 mass of the spire. In this region nearly the whole of the space 

 contained within the body-walls is occupied by the ovary, the 

 stomach, and the mass of the liver lying above and to the right 

 side of the stomach. It is only on the left side that some distinct 

 posterior prolongations of the hsemoccele are visible surrounding 

 the intestine, the left and lower sides of the stomach, and the 

 radula-sac. The great anterior hsemocoelic space surrounding the 

 pharyngeal bulb and the greater part of the coils of the intestine 

 is often refei-red to by writers on molluscan anatomy as the 

 anterior body-cavity, and allusion is sometimes made to a sort of 

 diaphragm or partition shutting off this anterior cavity from the 

 visceral cavity behind. In fact, there is no definite diaphr-agm or 

 dissepiment, and the appearance of one is due to a somewhat 

 complex union of muscular membranes connected with the kidneys 

 arrd genital ducts, but particularly to a large venous sinus with 

 muscular walls passing from the right towai-ds the base of the 

 ctenidium. In this space lies the elongated visceral ganglion. 



Theoretically the visceral haemocoele is to be regar-ded as a 

 continuous sj)ace, the hinder part of which is filled up by the 

 stomach and liver. This can be understood by reference to fig. 41, 

 illustrating a horizontal section through the ventral part of the 

 body of Neritina gagates. 



With regard to the ccelom, Lenssen observes with much truth 

 that in Neritina fluviatilis it is the most extensive space in the 

 whole body. " En avant," he says, " elle (la cavite pericardique) 

 se prolonge jusqu'a la base de la branchie, et de la, s'elargissant 

 de plus en plus en arriere, elle s'etend sur touts la largeur du 

 corps et divise I'animal en deux portions bien nettes. Sa parol 

 superieure se confond avec la base du rein et se prolonge sous 

 I'uterirs ; elle sepai-e le rein du foie. Sa partie inf erieure, chargee 

 ■de pigment, enveloppe le massif forme par les circonvolutions de 



