738 J. F. GUDERNATSCH 



RESUME 



The anatomy of the thyreoid gland of the Teleosts is decid- 

 edly different from that of most other vertebrates. It is not 

 an anatomical unit. The term 'thyreoid gland/ therefore, is 

 scarcely appropriate. Physiologically isopotent units are dis- 

 tributed over a wide area. Physical influences must be made 

 responsible for this distribution, which is due to mechanical 

 conditions of pressure and pull. 



If the thyreoid gland of the Teleosts really have its prototype 

 in the endostyle of the Tunicates, its phylogeny is somewhat as 

 follows. We have at first a uniform organ with a given function, 

 later a change of structure and function takes place, and the 

 organ loses its unity (Myxinoids and Teleosts). In higher forms 

 the new function is maintained but the organ retains its original 

 uniformity and integrity. 



The development of the organ from its anlage to the mature 

 state seems to be simpler in Teleosts than in higher vertebrates. 



The histology of the glandular elements of the thyreoid in the 

 Teleosts is but Httle simpler than in higher vertebrates. It shows 

 many parallels to the different features observed by numerous 

 authors in other thyreoid glands. 



The function of the thyreoid, concluding from its micro- 

 scopical appearance, must be closely the same in Teleosts as it 

 is in other vertebrates. 



