John Graham Kerr

“ The small placoid elements which cover the general body surface are seen to become enlarged at the margin of the mouth, especially posteriorly, these enlarged placoid elements functioning as accessory teeth and in fact being practically teeth in an early stage of evolution. ”

“ It is interesting to note also that the lining of the mouth still develops a covering of placoid elements. (In the typical gnathostome the placoid elements have of course disappeared from the mouth lining, except in the case of the functional teeth.) There is no oronasal groove in the adult, and the spiracle is greatly reduced. The valvular flaps guarding the external openings of the gill (6) cletts are much larger than in other sharks, particularly the most anterior (hyoidean) which meets its fellow ventrally and is prolonged backwards for some distance as an incipient operculum. ”

“ In the Skates and Rays the electrical disturbance is relatively small—imperceptible by human beings—but in Torpedo it is very considerable. No doubt the electric organs subserve a defensive function.
The kidney of the adult is a mesonephros. The pronephros is never functional, though it appears in a vestigial form in the embryo. The mesonephros shows a division into a broader posterior portion which alone is renal in function, and a slender anterior portion which in the male subserves a genital function. ”

“ The unpaired fins are obviously highly developed—the tail being almost homocercal with a lateral keel on each side as in various existing sharks, and it seems on the whole unlikely that the paired fins should be very primitive while the unpaired fins are so highly developed. ”

“ The lateral line organs on the sides of the body are situated at the bottom of an open groove; only in the head region has this become covered in.
The Notidanidae, like Chlamydoselachus, show more than the ordinary number of gill clefts. Notidanus griseus (Hexanchus) has six, while N. cinereus (Heptanchus) has seven postspiracular gill-clefts. In both Notidanidae and Chlamydoselachidae the vertebral column shows very primitive features with either very slight calcification or none at all. ”

“ This was a shark-like creature with the mouth apparently terminal. The body was covered with shagreen placoid elements: there were a series (five or seven) of gill slits on each side and the skull was probably hyostylic. The notochord was apparently persistent. The chief interest of Cladoselache, however, lies in its paired fins which are held by upholders of the “lateral fold” theory to be remarkably primitive. ”

“ The female genital duct is a typical Müllerian duct having at its anterior end a wide coelomic funnel and lined by glandular epithelium whose secretion forms adventitious coats round the egg during its downward passage. ”