1895.] AND AMPTJLLARX CAKAXS OF CHISI.WIA. 881 



canal across the throat, some distance behind the mandibular 

 branch. In all the specimens I have examined this branch runs 

 ventrally and backwards and then forwards, some distance from 

 the region of the fin, in fact quite close to the mandibular branch. 

 This condition was also common to the young examples. 



3. The Occipital CojiiiissuEE passes from the upward portion 

 of the main canal of the head and has a slight backward flexure. 

 Where the two sides meet there is sometimes a short median 

 backwardly directed branch (PI. LI. fig. 4, Oc.com.). 



All previous authors are agreed as to the open-grooved nature 

 of the canals in Chimcera, as distinct from the tubes found in 

 Callorhr/nchus, and yet the canals do not always persist as open 

 grooves in Chimcera or as closed tubes in CallorhyncJms. In young 

 examples of the former the canals are practically identical v^ith 

 those found in the adult ; but in two adult specimens which I 

 examined I noticed a portion of the lateral canal formed a perfect 

 tube, previous to its connection with the main canal of the head, 

 for a distance of about 27 millimetres. In the second specimen 

 the upper poi-tion of the sub-orbital branch was closed for about 

 12 millimetres. In neither case were there any signs of fusion, 

 so that it is probable that the borders of the groove coalesced in a 

 very early stage, or possibly they arose as distinct isolated tubes 

 and became united with the open groove later, as the isolated por- 

 tions of the canal do in more specialized fishes. In each case a 

 fine wire was passed through the tube and then a larger one, in order 

 to stretch it before it was finally cut thi-ough. In young specimens 

 of Callorhynchus short portions of the lateral canal occasionally 

 appear as grooves, the borders of which coalesce at a later stage 

 and form distinct tubes. 



3. Structure and Histology of the Canals. 



The minute structure of the canals and sensory organs is very 

 similar to that described in other fishes — e. g. Lcemargus and Raia, 

 Ewart(6 & 7) ; Amia, AUis (1) ; Polyoclon (3), — as a reference to the 

 transverse section of the lateral canal will show (PI. LI. fig. 5). 



In certain portions of the canal-system, viz., the supra- and sub- 

 orbital branches and the maxillary division of the maxillo-man- 

 dibular branch, there are a series of diamond-shaped openings, and 

 where these are present the canals are deeper and considerably 

 wider. Encircling these portions are a series of small cartilages 

 having the form of a broken hoop, the two broken ends termi- 

 nating as bulbous enlargements. Leydig (12) mentions that these 

 cartilages often terminate in dendritic branches, but I have not 

 observed this condition in any of the specimens I have examined, 

 in fact little or no variation was noted in either their size 

 or appearance. They measure 6 millim. in circumference and 

 1 millim. in breadth (PI. LIII. fig. 6). 



Solger (15) has carefully described the histology and certain 

 modifications of the canals and sense-organs. 



