54 
CIRCULATORY AND RESPIRATORY APPARATUS. 
With the exception of one dorsal and one ventral sinus the eir- 
culatory apparatus is wholly lacunar. The heart is apparently more 
or less sack-shaped with radiating fibres traversing part of its ca- 
vity and resembles in this respect the embryonic form of the heart 
in many other Gasteropods, such as it is described by GEGENBAUR 
(4). There is however a strong development of muscular tissue 
in its walls. 
In Neomenia the heart was not noticed by TULLBER« at least 
not recognized in its real character. Still I am convinced that 
the body y z which he describes and figures as being suspended 
inside his so-called egg-bag and which has been alluded to in a 
former chapter must really be looked upon as forming part of the 
eirculatory apparatus. I base this conviction 1) upon the fact that 
I find a body shaped and situated similarly to the one noticed by 
TuLLser6 both in Prof. v. Grarr’s and Ray LANKESTER’S sec- 
tions of Neomenia and that here this body is hollow and blood-cor- 
puscles are contained in the cavity, 2) upon the fact that in Prone- 
omenia I find a similar organ, similarly situated with similar con- 
tents, 3) that Kor£n and DANIELSsEn (16) who were the first to 
mention the presence of a distinet heart in these animals describe 
it as being situated in the posterior extremity ofthe body, between 
the integument and the intestine, i.e. in the same situation which 
the organs here alluded to are found to occupy in Neomenia and 
Proneomenia. 
The details of the anatomical and histological structure that can 
be made out from the sections of Neomenia and Proneomenia which 
I have as yet been able to examine are in many respects very in- 
complete. Although in Neomenia and Chaetoderma the heart is 
suspended in the pericardium (which at the same time serves, as 
was described above, for the passage outwards of the genital pro- 
ducts) it is in Proneomenia for the greater part applied against the 
dorsal wall, and inferiorly projeets into the pericardial cavity. This 
inferior wall is partly muscular, the fibres erossing in different di- 
