780 report— 1884. 



2. Secondary Astragalus. — Three cases were shown in which the small process 

 overhanging the os calcis and external to the groove for the flexor longus pollicis 

 tendon was separate from the astragalus. In all three cases these ossicles were 

 connected with the posterior fasciculus of the external lateral ligament of the 

 ankle-joint. 



ti. Double Superior Vena Cava. — Three examples of this anomaly were exhibited. 

 Two occurred in females, one in a male. The transverse innominate vein in all the 

 cases was of small size, and the left cava (persistent left duct of Cuvier) was 

 continuous with the coronary sinus. 



■9. On the Presence of Eyes and other Sense Organs in the Shells of the 

 Chitonidm. By Professor H. N. Moseley, LL.D., F.B.S. 



The Chitonidae have hitherto been regarded as characterised by an entire 

 absence of organs of vision, the presence of eyes in the shells of numerous genera 

 having been entirely overlooked by naturalists. The author first discovered the 

 eyes in a specimen of Schizochiton incisus dredged by Captain Chimmo, R.N., in 

 the Sulu Sea, in which species they are larger and more conspicuous than else- 

 where, and on examining carefully the shells of certain other forms found eyes 

 present there also. The eyes are entirely confined to the shells, and to the exposed 

 parts of these the ' tegmenta,' not occurring at all on the ' articulamenta.' They 

 never occur on the girdle or zone or any other part of the mantle. They appear as 

 bright, highly refracting convex beads on the shell surfaces, encircled by zones of 

 dark pigment formed by the pigment layers. The eyes are usually circular in out- 

 line and very minute, measuring in Schizochiton incisus about jyg of an inch in 

 diameter, in Acanthopleura spiniyer s l- of an inch, and in Corephium aculeatum, 

 in which they are oval in outline, v }- of an inch by about -j^. 



In the case of all the intermediate shells, the eyes are confined to the areae 

 .laterales, or to the lines of demarcation between the arena laterales and the area 

 centralis, which latter is usually entirely devoid of them. 



In some genera of Chitonidae, such as Acanthopleura and Corephium, the eyes 

 appear to be often destroyed and obliterated in the older regions of the shells by 

 decay and delamination of the tegmental surface, or its destruction by boring alga* 

 or animals. They are, however, constantly re-formed by the mantle in the process 

 of growth of the shell at the growing margin of the tegmentum, and may be 

 observed in this situation in all stages of construction. 



In other genera, such as Tonicia, the eyes lie in shallow pits of the shell surfaces 

 and thus escape destruction by wear, nearly the entire number which have been 

 formed being thus found present in fully grown shells. The tubercles and pro- 

 minences by which the tegmenta are covered in some forms serve perhaps as pro- 

 tection to the eyes from attrition. 



The entire substance of the tegmentum in the Chitonidae is traversed by a series 

 of branching canals, which are occupied in the living animal by corresponding 

 ramifications of soft tissues and nerves. The strands of soft tissue are continuous 

 with the tissues of the mantle along the line of junction of the margin of the 

 tegmentum with the upper surface of the articulamentum, by means of a series of 

 tubular perforations in the shell substance. Further, in the intermediate shells of 

 most genera, there are a pair of lateral slits (incisures laterales), one on either side, 

 in each shell in the lateral laminae of insertion ; these slits lead each to a narrow 

 tract in the deep substance of the shell which follows the line of separation between 

 the area centralis and area lateralis. This tract is permeated by longitudinal canals, 

 into which open a series of fine apertures on the under surface of the shell. By 

 these apertures numerous nerves enter the tract from the bed of the shell, and 

 traversing the longitudinal canals give off a series of lateral branches on either side 

 from it to the network within the tegmentum. In the cases of the anterior and 

 posterior shells there are usually a considerable number of slits present in the 

 Laminae of insertion, each connected with a similar nerve-supply to the teg- 

 mentum. 



