634 FRANCIS M. BALDWIN 



slight marginal membrane about the layer of cuboidal cells is 

 noticeable, in others apparently there is none. 



The follicles are more numerous throughout the central region 

 of the gland than at either extremity, and they are separated 

 from each other by conspicuous spaces (large or small in com- 

 parison to the individual follicles of the region) in the connective 

 tissue in which they are imbedded. These spaces for the most 

 part are lymph vessels, although here and there are small veins 

 (especially those returning blood from the geniohyoideus and 

 sternohyoideus muscles), which unite with the inferior jugular 

 vein in this region as pointed out above. This complex of fol- 

 licles, lymph spaces, blood vessels and loose cells and strands of 

 connective tissue, is maintained in the central portion of the 

 gland, but at the two extremities, these relat'ons are not so 

 conspicuous. 



So far as I have observed, there is no good evidence that either 

 the inferior jugular vein, or the smaller twigs from the muscles 

 break up into a 'retemirabile' n this region, a fact which, when 

 taken in connection with conditions in later larva stages is of con- 

 siderable interest, and concerning which more will be said below. 

 No attempt is made here to describe the histological relationships 

 of the parts in the thyreoid gland. The gland changes but little 

 in the succeeding larva stages, and hence but little space need 

 be given to it. 



G. Amblystoma larvae, 26 min. long. In the 26 mm. larvae the 

 gland is distr buted along the inferior jugular vein for a distance 

 of 350 or- 400 microns. A few isolated follicles lie in the same 

 section with the anterior wall of the ear, and on the right side 

 these lie some distance medial to the inferior jugular vein. There 

 is no regularity in the arrangement of the follicles on either side. 

 Most follicles have conspicuous lumina, but as yet these contain 

 no colloid. The lymph spaces are somewhat larger and more 

 prominent, but otherwise there are no great differences from the 

 19 mm. stage. 



H. Amblystoma larvae, 35 mm. long. The thyreoid in the 35 

 mm. larva has elongated, now being between 450 and 500 micra in 



