466 Afiscellaneous. 



On the Heart o/Dentalium. By Dr. L. Plate, Marburg. 



In " Bemerkungen zur Organisation der Dentalien " (Zool. Anz. 

 1888), published rather more than two years ago *, I adopted tho 

 view expressed by Lacaze-Duthiers in his classical treatise ou the 

 Scaphopods, that these peculiar Mollusks do not possess a heart, but 

 that the blood is driven along in the lacunae by the contractions of 

 the musculature of the body-wall only. Subsequent investigations 

 have shown me that this assertion does not correspond with facts, 

 but that a heart, albeit a rudimentary one, is actually present, lying 

 in a special pericardium. The possible existence of the latter has 

 already been suggested by the above-mentioned French anatomist. 

 It is well known that the largest of all the blood-spaces, the so- 

 called sinus abdominalis, runs along the median line of the ventral 

 side of the body. At the anterior end of this, a little behind the 

 anal opening, there is a hemispherical projection of the body-wall 

 into the pallial chamber. This protuberance, which is marked p 

 by Lacaze-Duthiers in plate ii. fig. 2 of his paper (' Annales d. Sc. 

 nat. Zoologie, ser. 4, t. vii. 1857), is produced by the completely 

 closed pericardial sac, the ventral wall of which unites intimately 

 with the integument, while the dorsal wall is applied to the 

 stomach and the two nephridial sacs. Since Lacaze-Duthiers natu- 

 rally did not succeed in filling the pericardium with colouring- 

 matter by injection from the abdominal sinus, he remarks with 

 justice : — " It therefore seems to me reasonable to admit that this 

 sac is closed, and that it perhaps represents a rudiment of a peri- 

 toneal, pericardial, or some sort of serous cavity." ISTow in this 

 chamber there lies the heart, in the shape of a rounded thin-walled 

 pouch, which is not further divided into auricle and ventricles. 

 The degenerate condition of the heart is expressed in this simplicity 

 of structure and in the entire absence of vessels provided with 

 special walls and of reno-pericardial openings. The heart is 

 nothing more than a sac-shaped invagination of a portion of the 

 dorsal pericardial wall into the lumen of the pericardium. The 

 blood-corpuscles find their way into it, since they pass from the 

 abdominal sinus into narrow fissures which lie between the stomach 

 and the dorsal wall of tho pericardium, and which are due to the 

 fact that the two latter are united together only in places. From 

 these fissures they fall into the heart itself, when the invagination 

 takes place. When the heart contracts they aro driven into similar 

 fissures which are situated between the dorsal wall of tho pericar- 

 dium and the nephridia, and so find their way into the perianal 

 sinus. Into histological details I will not at present enter ; I may 

 only remark that the histological structure is the same in the peri- 

 cardium as in the wall of the heart itself, and that there exist in 

 both numerous muscular fibres lying parallel with one another and 

 arranged in rings. Nevertheless the contractions appear only (or at 



* The present paper was sent in Feb. K, 1890. 



