674 PROFESSOR FRANK J. COLE 



on the component elements of the skeleton until its developmental history has been 

 worked out. Stockard (30), the only writer who has published on the development 

 of the Myxinoid skeleton, makes no reference to this point. 



In fig. 3 of my first part a cartilage cell is shown containing four nuclei, and others 

 with two each. This must not be confused with one of the phases of chondro-mucoid 

 degeneration of the cartilage cell described by Schafper, in which spaces appear in the 

 sarcode containing chondro-mucoid granules. These spaces with their contents simulate 

 the appearance of nuclei, but may easily be distinguished from them. 



The parachordal cartilages (pc.) represent a chondroidal deposit between the elastica 

 externa and the skeletogenous layer of the notochord. This deposit is generally of a 

 uniform shape, but varies in the extent to which it may be prolonged backwards. The 

 posterior extension usually follows three lines — a median ventral one and a pair of 

 dorso-lateral ones. Occasionally the parachordal dies away in detached nodules of 

 cartilage, This is shown on the right side of fig. 2. 



The hypophysial plate (h. p.) consists predominantly of soft cartilage, but the 

 anterior half of the forward handle may be formed of hard cartilage, and probably in 

 all cases there are nests of hard cartilage here and there in this part of it. The 

 posterior end of the central plate is usually more or less ragged, and the posterior 

 handle is always fenestrated — all the fenestrations being correctly shown and located 

 in fig. 2. Owing to its V shape, its true width cannot be shown in the figure, being, of 

 course, much greater than appears. The outline in fig. 2 was obtained by measuring 

 across the tips of the V. 



The inferior lateral cartilage (i. I. c.) may terminate in a pointed rod behind the 

 second branchial arch, as shown in fig. 1, Part I. ; but more usually there is only 

 a posterior blunt projection here, and a corresponding anterior one into the fourth 

 fenestra (/.*). On the right side of fig. 2 is shown a small perforation at this point. 



In my first part it is stated (p. 763) that the lower division of the second 

 "branchial" arch (br. a. 2 ) is not always present. It was not found by Parker, but 

 is figured by P. Furbringer and Neumayer, and Schaffer (28, p. 242) apparently 

 never found it wanting. As stated in my previous paper, it was present in all my 

 series of sections without exception. Owing to its close connection with the posterior 

 segment of the basal plate, it is not usually noticed in dissections unless specially 

 looked for, and I now feel disposed to regard my former statement as erroneous, and to 

 believe that the lower division of the arch is invariably present. I feel the less certain 

 about this, however, since I am able to record one surprising variation in this arch. 

 Ayers and Jackson describe in Bdellostoma for the first time a fusion between the 

 posterior extremity of the lower division and the inferior lateral cartilage, thereby 

 eliminating the break in the course of the arch present in Myxine. This was not found 

 in Bdellostoma by either J. Muller or Parker, but since my first part was written 

 I have found it once in Myxine. It is interesting to record this important variation, 

 since it must be a very rare one, nor is it one that could be easily overlooked. 



