474 Prof. Reid on the Vogmarus Islandicus. 



tion posteriorly, and in fact constitutes the chief and character- 

 istic part of the tubercle. In stripping off the subjacent layer of 

 the skin, some of those minute masses constituting the chief part 

 of these tubercles may adhere so firmly to it as to be torn off along 

 with it. The bands forming the network are composed of fibres 

 so very closely aggregated, that it is only after they have been 

 mechanically separated that the fibres become distinctly visible. 

 2. The lower layer of the chorion is composed of a dense areolar 

 tissue assuming an aponeurotic appearance, the fibrous arrange- 

 ment of which is very apparent under the microscope. These 

 fibres can be readily separated from each other, and are arranged 

 in two distinct layers, in each of which the fibres run parallel to 

 each other, and cross those of the other layer at right angles. It is 

 this aponem'otic portion of the skin which is prolonged inwards 

 among the muscles to form intermuscular septa, and to assist in 

 the formation of the muscular sheaths previously described. Pro- 

 perly speaking this aponeurotic layer ought not to be described 

 as constituting a portion of the chorion, but it is so closely united 

 to it, that it requires a careful dissection to separate them. The 

 difference between the texture forming the netwoi'k and the ex- 

 ternal covering of the tubercles in the upper layer of the chorion, 

 and the aponeurotic fibres constituting what we have just de- 

 scribed as the lower layer of the chorion, is very marked when 

 the polarizing prisms have been fixed in the microscope, from the 

 very dissimilar colours which these two textures then exhibit. 



The skeleton did not contain any osseous texture, but was 

 composed of cartilage, of fibrous tissue, and of a remarkable 

 structure which was entirely new to me. True cartilage was 

 found in some of the bones of the head, in the upper ends of the 

 interneural spines, in the articulating discs of the dorsal fin rays, 

 and in the vertical cartilaginous plate at the end of the caudal 

 vertebrae. None of the vertebrre contained any true cartilaginous 

 tissue, except the fifty-ninth and sixtieth, in which the gelatinoiis- 

 looking substance in the cup-shaped cavities was changed into 

 true cartilage, and which also presented the other peculiarity 

 already pointed out of being considerably shorter than those im- 

 mediately preceding and following them. The cartilaginous plate 

 at the end of the caudal vertebrae, the upper extremities of the 

 interneural spines, the articulating discs of the dorsal fin rays, 

 and the bones of the head previously enumerated were entirely 

 composed of true cartilage, while some of the bones of the head 

 were composed of true cartilage internally, and were covered ex- 

 ternally by a layer of the peculiar textui-es about to be described. 

 True cartilage, as has already been mentioned, exists in the dermo- 

 skeleton, viz. in the warty-looking tubercles attached along the 

 lower margin of the body of the animal. The relative amount 



