5G4 



ANATOMY OF VERTEBRATES. 



the forms have been described as l an epithelial stratum, con- 

 sisting usually of nuclei set closely together in a scanty basis 

 substance, fig. 435, which is either feebly granular or of a 

 somewhat oily aspect : ' ( their nucleoli are not always visible, 

 and vary in number from one to four or five. The nuclei are 

 always vesicular, bounded by a strongly marked envelope, and 

 have a mean diameter of oVnth inch.' l But the formed lining 



435 



436 



Formifled proteine, lining a vesicle of 

 the thyroid, Hedgehog, cccxxix. 



Formifled proteine, lining thyroid vesicles, 

 Bullock, cccxxix. 



substance often presents, as in figs. 435 and 437, the condition 

 of delicate vesicles, without nucleus, with contents mostly pellucid, 

 sometimes faintly granular. Dr. Jones observes : — ' I am inclined 

 to believe that they originate in the nuclei, which undergo a kind 

 of expansion, at the same .time losing their nucleoli.' Emanci- 

 pating himself for a moment from the ( generative ' theory in 

 reference to the ( progress of the nucleus from its primitive con- 

 dition to a further stage of cell-development,' he candidly admits 

 it to be ' worth remarking that it ' (the stage) ' may be artificially 

 produced by adding to the specimen some coagulating reagent, 

 which speedily solidifies a film of albuminous plasma around the 

 nuclei, and thus produces very good imitations of cells.' 2 



Analyses of the contents of the thyroid have shown or rendered 

 it very probable that they are albuminoid, yet not in the state of 

 ordinary fluid albumen, and that gelatine is sometimes an in- 

 gredient : among the salts are chloride of sodium and a trace of 

 alkaline sulphate : crystals of triple phosphate and of oxalate of 

 lime occur in the cavities. 3 



In the Ornithorhynchus two bodies, extending between the 



1 cclxxix. p. 1104. 



2 lb. p. 1105. For the conditions and degree in which this and most other pheno- 

 nomena of so-called ' cell-development ' may be artificially manifested, see ccix" and 

 ccx", especially the latter important contribution to the philosophy of physiology. 



3 cclxix. p. 1106. 



