105 



timate connection, both tube and connected gland were carefully re- 

 moved from the surrounding cartilage. The tube was about two milli- 

 metres in length and a little more than one millimetre in width. It 

 increased slightly in diameter towards its point of attachment to the 

 thyroid gland. It was open at its anterior end to the oral cavity and 

 here its lining became continuous with the mucous membrane covering 

 the dorsal surface of the basihyal cartilage. 



Tube and gland were stained in bulk in borax-carmine and pre- 

 pared for sectionising. Sections were cut in a vertical longitudinal 

 direction so as to obtain a series passing completely through the 

 central part of the tube and the gland. An examination of these sec- 

 tions, a portion of one of which is shown in Fig. 2, showed that the 

 gland had the usual structure of the thyroid body, being composed 

 of numerous follicles, 

 each one lined with a 

 columnar glandular 

 epithelium. The fol- 

 licles are separated '^Z; ^^ i": b^"^ 

 from one another by ; ^ "^ '' ' -P <^^ 

 strands of connective vlr"^^ c' ° 0*oVjf. --"fe, 

 tissue in which there .-i ^^d'o^'^' 

 are scattered cells '*'^' c ^'^\ (\°' ' 

 having deeply staining ,, ^^^^isfi^o 

 nuclei. c? - ' 



The tube is closed tt- o ^r _*• i i •* ^- i , • ■ ^ t. 



J^ig. i. Vertical longitudinal section of vestigial tube 

 at its lower posterior and thyroid gland of Chlamydoselachus anguineus X 18. 

 end by a strong Sep- *•«• Wood vessels, d denticles, e. enamel organ, /.o. 

 •' or- follicles, l.t. lumen of tube. v.t. vestigial tube. 



tum of connective 



tissue which binds it very closely to the anterior end of the thyroid 



gland. 



Internally it is furnished with an ectodermal lining in which there 

 are small dermal spines or denticles. These denticles are in very interesting 

 condition. They are incompletely developed and resemble some of 

 the early developmental stages in the growth of ordinary dermal 

 spines. Each consists of a papilla of cutis and covering this, there 

 can be distinguished in many of them, a definite layer of cells, con- 

 stituing, I think, the enamel organ. Above the latter are the other 

 layers of ectodermal cells. The mucous membrane lining the mouth 

 and pharynx is also furnished with numerous small denticles, and on 

 microscopic examination these are found to be completely developed, 

 recurved spines, thus differing from those found in the lining of the 



