The wal! of the precloacal organ is formeel as in the other Neomenidae and as that oi 

 the end-funnel of the cloaca-ducts of Chaetodcrma (Wirén 6 a ). The precloacal organ is small 

 and opens into the cloaca through a small opening (fig. 5). 



The above mentioned copulation-spicula are in communication with the cloaca in the 

 nart indicated 1>\ c (fig. 19—21, 7 — 9 es). Their direction is proximal above the ventral nerve- 

 stems and they extend to some distance anteriorly (cf. Proneomenia vagans, Kow. and Mar. 2). 

 They are either round organs, triangular or somewhat square, apparently calcareous. Such a 

 calcareous spiculum is surrounded by a firm distinctly staining cuticula ; around this a layer 

 of epithelium-cells is found. Regarding its formation the following facts should be mentioned. 

 cellular envelopment increases in bulk considerably at the basis of the spiculum ; here the 

 cells become high and cvlindrical and are of a peculiarly threadlike structure (fig. 20b). In this 

 epithelium-bag is enclosed a cuticular mass (fig. 20c") which is continuous in the attenuated 

 cuticular layer around the spiculum. This mass is very finely fibrillar, the fibres being in continuity 

 with those of the cells of the bag. Upon this mass a little column d is found, built up of cells 

 and continuous in a very transparent part, in which some nuclei are perceptible. This transparent 

 column is not long; around this we find the basis of the proper spiculum, of which after 

 decalcification nothing is visible. Moreover the spiculum is sustained at the basis by a hard 

 ring t\ which is structureless and stains obviously. An attenuated circular muscular layer a 

 surrounds it entirely. The relation between the said parts and the calcareous spiculum cannot 

 be discovered. To the basis of the spiculum are attached long strong protractors (cf. fig. 19) 

 enveloping the spiculum and attaching themselves to the clistal body-wall ; (fig. 21 A, p~] and 

 also strong but shorter retractors, fixed to the ventral and lateral body-wall (/'). Fig. 2 1 B 

 shows the shape of a copulation-spiculum, after isolation with Eau de Javelle. 



We must not overlook the presence of a pre-anal gland around the cloaca (fig. 6 — 8), 

 the structure of which may be compared with that of Proneomenia neapolitana (Thiele 8). 



Examination of the heart can be properly made when this is in diastole at the death 

 of the animal. The median walls of the pericardial prolongations invaginate (fig. 22 A); these 

 invaginations increase in size and as soon as both offsets have united, the invaginations coalesce 

 and form together the atrium (fig. 22 B, a). This atrium, which has consequently a distinct 

 doublé origin, is open distally and dorsally. Then there is also a ventricle : an invagination ot 

 the pericardium, with trucker wall (C, v). This interpretation of atrium and ventricle is the more 

 justifiable on account of two points of communication between both, which can be indicated ; 

 at those points the wall is much thicker and apparently forms a sphincter (D). The same 

 arrangement obtains in other Solenogastres, which I hope to describe afterwards. In other forms 

 atria are also demonstrated (Hubrecht 2). To me it seems that it should be interpreted in this 

 way : the heart of the Solenogastres is undergoing marked reduction, a reduction running parallel 

 to that of the gills and gill-veins ; an opinion also enunciated by Thiele. This opinion is 

 preferable to that of Heuscher (5), who considers the heart of Proneomenia Sluiten to be in 

 an embryonic condition. It must be owned that the facts hitherto known concerning the structure 

 of the heart cannot be Iooked upon from one point of view ; close investigations, especially 

 in comparison with Chaetoderma, are very desirable. 



