564 



ANATOMY OF VERTEBRATES. 



375 



insoluble in alcohol, and slightly reddens litmus paper: it long 

 retains its noxious property. Against this the mucous surface of 

 the alimentary tract is proof: the poison, to take effect, must 

 enter the current of the blood. Here it is ordinarily introduced 

 by the puncture of the poison-fang, but it takes effect by applica- 

 tion to an abraded surface. The poison affects the nervous 

 system ; death is usually preceded by spasmodic convulsions, and 

 followed by speedy putrefaction. 



103. The Thyroid Body or Gland of H&matocrya.- - In the 

 Skate (Raia) the body which seems to have best claim to be 



regarded as a thyroid is situated sternad 

 of the terminal division of the branchial 

 artery, of a reddish-grey colour and con- 

 glomerate exterior. It consists of nume- 

 rous, mostly subspherical, vesicles, of from 

 g^- to T j- T inch diameter, fig. 375, having 

 a structureless tunic, A, lined by a thick 

 stratum of epithelial substance, consist- 

 ing of nuclei and granular matter, B. Dr. 

 Handfield Jones, who has given the above 

 result of microscopical investigation of this 

 ductless gland, also found, in the Skate, 

 ' at some distance behind it, just at the 

 junction of the branchial arches anteriorly, 

 a small light reddish mass, which was 

 covered by a thin fascia, and by mucous membrane.' 1 It consisted 

 ' of vesicles about ^-j-g to y^- inch diameter,' fig. 376, ' formed 



by a structureless " limitary ' 

 tunic, thickly lined by epithelial 

 substance, and containing abund- 

 ance of nuclei and granular matter, 

 with a few cells. The pseudo- 

 branchia, situated on the anterior 

 wall of the spiracular canal, is 

 manifestly of entirely different 

 structure to the organs described. 

 It consists of small plica? of mucous 

 membrane, covered by a kind of 

 pavement epithelium.' 2 

 In the Menobranchus the thyroid is represented by two 

 symmetrical bodies, situated at the sides of the basibranchials. 



1 CCLXXXIX. p. 1110. 2 Ib., and see CXLV. p. 270, with reference to the non- 



thyroid nature of the pseudo-branchiae in other fishes. 



Vesicle from thyroid of Skate. 

 CCLXXXIX. 



376 



rrfs- 



Vesicle from accessory thyroid of Skate, diam. 

 In. CCLXXXIX. 



