652 FRANCIS M. BALDWIN 



clump in the mid-line in front of the halves ; these Maurer inter- 

 prets as remnant of the isthmus and calls it 'Nebenschilddriise' or 

 'accessory thyreoid.' For a time it is difficult to follow the two 

 halves in their subsequent development because of their loss of yolk 

 content. (The writer has had the same difficulty in his material 

 of Amblystoma of this stage) . Cells arrange themselves in a solid 

 cord on either side of the sternohyoid muscle. Later, (three or 

 four weeks) these cell cords develop into follicles which show the 

 presence of colloid. The external jugular vein lies a little ventral 

 to the thyreoid in the adult, but the wonderfully complex network 

 of blood vessels, of the adult does not develop in the larval stages. 



He found the development of the thyreoid in Siredon pisci- 

 formis and Salamandra maculata similar to that in Triton 

 taeniatus, and hence he concludes that the latter species fur- 

 nishes a good example of the development of the organ in the 

 uro deles in general. 



Miss Piatt ('96), finds one or two points of difference in Nec- 

 turus maculosus, from the description given for Triton by Maurer. 

 In Necturus, the thyreoid arises from the ''base of the hyo- 

 mandibular pocket, (not from the second, as stated by Maurer) 

 directly above the oral fusion, and extends backward below the 

 ventral aorta to a point where the mesoderm of the hyoid and 

 mandibular arches unite in the medial plane" (p. 561). In addi- 

 tion, ' 'the cells separate from the anterior part (isthmus of Maurer) 

 of the outgrowth, are taken into the mylohyoideus muscle and do 

 not form accessory thyreoid" (p. 567). The cells of the posterior 

 portion are divided into two lines, and form neither solid massfes or 

 closed vesicles, and later (46 mm. larva) they constitute a mass of 

 vesicular tissue (thyreoid proper). 



Bolau ('99) gives a description of the position of the thyreoid 

 and thymus glands in adult amphibians, but has no account of 

 their development. Livini ('02), describes the development of 

 the thyreoid gland in Salamandrina perspicillata, which, in its 

 essentials, closely accords with Maurer' s account of Salamandra 

 maculata. He confirms the solid condition of the early anlage, 

 typical of the urodeles. Maurer ('02) in Hertwig's Handbuch, 

 gives briefly the results of his earlier work ('88), and mentions, in 



