60 



with the lower jaw. These cartilages exist in other forms and have 

 been noted by Gegenbaur. 



Hitherto so far as I am aware no cartilages have been found 

 in the position of those which I have recently discovered in Hexan- 

 c h u s and LaBmargus, but I am aware that Dohrn ^ ), van Wijhe '■^) 

 and Beard ^) have postulated for various reasons the former existence 

 of an arch and additional gill-cleft between the mandibular and hyoid 

 arches, and it is just possible that the cartilages in question in front 

 of the basihyal may be the remains of the missing arch. On the 

 other hand it is possible that these cartilages may represent the 

 remains of lower elements in the mandibular arch which have been 

 thrown out of position and have degenerated. I have not as yet been 

 able to read what Dohrn and van Wijhe say on the matter and 

 until I have studied the subject further it is impossible for me to 

 pronounce any definite opinion. A satisfactory explanation cannot 

 probably be expected until embryos have been obtained. In the 

 mean time an examination of the condition of the cartilages in a 

 number of specimens and a further investigation of the seventh cranial 

 nerve may throw some light on the matter. 



I do not know whether the cartilage at the lower end of the 

 hyomandibular in Laemargus is in any way associated with the 

 series in front of the basihyal but its origin should be inquired into. 



It is possible when sharks of other species are carefully examined 

 traces of these cartilages may be found. The Director of the Naples 

 Zoological Station has kindly promised to send me heads of Heptan- 

 chus when these can be secured. I should expect at any rate to 

 find vestiges of the cartilages there. 



Before closing I have to record the presence of a basimandibular 

 cartilage (Fig. 2 Bm) in one of my specimens ofHexanchus. I have 

 already pointed to its existence in LaBmargus, and the matter has 

 interest attaching to it *). 



I take the opportunity of thanking Mr. W. R. Griffith for the 

 drawings he has made from my dissections. 



1) DoHEN, Studien zur Urgeschichte des Wirbeltierkörpers, No. VII. 

 Mitteil. a. d. Zool. Stat. zu Neapel, Vol. 6, Part 1. 



2) VAN "Wijhe, Ueber die Mesodermsegmente und die Entwickelung 

 der Nerven des Selachierkopfes, Amsterdam 1882. 



3) Beaed, The System of Branchial Sense Organs and their Associated 

 Ganglia in Ichthyopsida. Quart. Journ. Micro. Sei., Vol. 26, p. 103 et seq. 



4) HowEs, Basi-mandibular Elements in the Vertebrata. Proc. Zool. 

 Soc, 1891, p. 158. 



