THYKEOID GLAND OF THE TELEOSTS 723 



according to Maurer it must have been rather old, yet it measured 

 only 30 cm. long. 



Maurer's observations do not accord with the conditions I 

 find in rainbow-trout four weeks old, nor in 25-30 cm. brook trout. 

 As before stated, there is no paired arrangement of the thyreoid 

 clusters, and the follicles are also in many cases distantly removed 

 from the stem of the aorta. Other differences may be either 

 due to specific or individual variations. Maurer's statements 

 would indicate that the thyreoid gland tends to preserve its origi- 

 nal unity, being finally broken up by force. My observation, how- 

 ever, seems to show the contrary, at least in Salmo irideus and fonti- 

 nalis. In individuals one year old the follicles are more densely 

 packed than in those one month old, although the intervening 

 spaces have grown larger. The follicles also have become more 

 numerous. This seems to warrant the supposition, that the thy- 

 reoid elements are disassociated at an early stage and subsequently 

 multiply. 



The multiplication of the follicles is described by Maurer as 

 being very simple. While the epithelial cells are increasing in 

 number after the forty-first day (in trout) solid buds appear on 

 the primary vesicle, which very soon form central cavities and 

 then pinch away. We do not know whether a similar process is 

 maintained in later life, follicles coming from follicles, or whether 

 new follicles are derived only from primary epithelial cells multi- 

 plying and forming a lumen. The latter supposition would more 

 readily explain the scattering of thyreoid elements, germ elements 

 I might say, to distant regions. L. Miiller believes the new folli- 

 cles to originate from old ones by buds from the epithelium which 

 are subsequently pinched off. Baber contributes an interesting 

 observation in the conger eel where in the wall of large follicles 

 small ones sometimes lie imbedded so deeply that the epithelium 

 between them is flattened out. Baber thinks that at times the 

 wall breaks through and the two lumina are united. In other 

 cases, however, the small imbedded follicles grow out and become 

 independent. 



The epithelial tubes found in the thyreoid of higher vertebrates 

 as transitory growth stages are absent in the Teleosts. In the 



