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 Hamatocrya. — 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 nmne- 

 rous, mostly subspherical, vesicles, of from 

 "sV to xla- iiich 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.'' It consisted 

 ' of vesicles about -pio to -^ 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 spiracnlar canal, is 

 manifestly of entirely different 

 structure to the organs described. 

 It consists of small plic;\3 of mucous 

 membrane, covered by a kind of 

 pavement epithelium.' - 

 the Menobrancluis the thyroid is represented liy two 

 symmetrical bodies, situated at the sides of the liasibranchlals. 



Tesicle from thyroid of Skate. 



CCLXXXIX. 



376 



side from arccsHory thyroid nf Skate, diam, 

 j^ In. CCLXXXIX. 



In 



' OCI.XXXIX. p. 1 no. = lb., an.l see oxlv. p. 



thyroid nature of the pscmlo-hrancliias in other fishes. 



70, with reference to the non- 



