WtM 



i, . . 



^■fii^ 



780 



llEPORT — 1884. 



il«I 



2. Scoomlnry Asfrn(jahis. — Three cases were shown in which th-' small proce.y 

 overhanging' the os cah-is and external to the groove for the fj< xnr loiifrus polHcis 

 tendon was separate from the a.-tragalus. In all three cases tin-.-j ossicles were 

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

 «nkle-joint. 



y. Double Superior Venn Cum. — Threeexamplesof this anomaly were cxiiiljited. 

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

 ca.ses was of small size, and the left cava (persistent left dnct of Cuvier) was 

 continuous with the coronary sinus. 



9. On the Presence of Ei/es and other Sem": Orcjans in the Shells of th; 

 Chitontdte. By Professor H. N. Moseley, LLJ)., F.RS. 



The (^hitonidnc have hitherto been rcfjavded as characterised by an entire 

 absence of oi-pans of vision, tlie presence of eyes in the shells of numerous irenera 

 having been entirely overlook^'d by naturalists. The author lirst discovered the 

 eyes in a specimen cf Sc/iizoc/iifon j«m!(.y dveil'red by Captain ('himmo, R.X., in 

 the Suhi Sea, in which species they are larp'er and more conspicuous tlian else- 

 where, and on examinin<r carefully the shells fi 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 occurrir.tr v.t all on the 'articulamenta.' They 

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

 bright, highly refracting convex beads on the sb.ell 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 SrliizDckitim inrisus about j'-; of an inch in 

 diameter, in AcanfJuiplvnra spinii/er ,,l, of an inch, and in Curephium acnleatum. 

 in which thev are oval in outline, ,.l, of an inch l>v about ,'-,. 



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

 lalerales, or to the lines of demarcation between the areje laterales and the area 

 centralis, whieli latter is usually entirely devoid of them. 



In some genera of ( 'hitonida;, sncii as Acant',:oid<'ura and Corephiuiu, the eyes 

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

 <lecay and delamination of the tegmental surface, or its destruction by l)oring alg;e 

 or animals. They are, however, constantly re-furmed liy the mantle in tlie proce.^ 

 of growth of the shell at the irrowing margin of the tt^gmentum, and uiny be 

 observed in this situation in all stau'es 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 no in1)er which have been 

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

 minences by which the tegmenta are co\ered in some forms serve perhaps as pro- 

 tection to the eyes from attrition. 



The entire substance of the tegni(>ntum in the Chitonidte is traversed by a series 

 of branching canals, which are occupied in the living animal by correspond;!),' 

 ramifications of soft tissm's and ner\('s. The strands of soft tissue are coutinuoiLs 

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

 tegmentum with the npvier surface of the artieulamentum, by means of a series of 

 tubular perforations in the shell snl)stance. Further, in the intermediate shell." oi 

 most genera, there are a pair of lateral slits (iucimrcc laternlcs), one on either side. 

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

 tract in the deep substance of the .slioU whicli follows the line of separation between 

 the area centralis and area lateralis. This tract is permeated by longitucilnal canal?, 

 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 ."^eries of lateral branches on either side 

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

 posterior shells tlif^re are usually a considerable number of slits present in the 

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

 mentum. 



i: 



