318 INEZ WHIFFLE WILDER. 



leading dorsally from the roof of the mouth, from a point a 

 little anterior to the posterior nares. During the premetamor- 

 phic period of mitosis and glandular development, the inter- 

 maxillary gland becomes enormously enlarged and complicated 

 and fills the space between the two maxillary bones with its mass 

 of convoluted tubules. 



The tongue possesses no multicellular glands until, with the 

 approach of metamorphosis, large numbers of tubular glands 

 (Igl, Fig. 22, c] appear opening in the more distal region of the 

 tongue upon its dorsal surface, and transforming the tongue into 

 a glandular mass. The development of both intermaxillary and 

 lingual glands at this time is, of course, suggestive of a prepara- 

 tion for the terrestrial life of the adult. By means of their 

 secretions the mouth is kept moist both for its respiratory 

 function and to render more sure the capture and retention of 

 terrestrial prey. 



'Among the most significant of the structural changes involved 

 in metamorphosis are those concerned in the atrophy of the 

 gills and the modifications of their associated structure, the 

 visceral skeleton. Externally changes do not occur in the gill 

 bushes themselves until within a few days of the completion of 

 metamorphosis. Then the filaments become shorter and more 

 rounded, and the whole structure undergoes rapid shrinkage and 

 atrophy. As the gills are merely blood vessels covered with a 

 thin layer of epidermic cells, the withdrawal of the blood from 

 them so reduces them in size that the process of atrophy can 

 take place very quickly. 



The metamorphic changes in the visceral skeleton consist 

 mainly in the atrophy of the distal end of the first epibranchial 

 and the atrophy of the whole of the second, third, and fourth 

 epibranchials (Figs. 23, 24, and 25). The process begins at the 

 time of the premetamorphic mitotic period, and appears first in 

 the distal ends of the epibranchial cartilages where the hyaline 

 matrix becomes dissolved around the groups of cartilage cells 

 (Fig. 23, 6). With the atrophy of the free ends of the epibran- 

 chials, there occurs that shortening of the gill region which is 

 mainly responsible for the decrease in the proportionate length 

 of the head as the animal passes from larval to adult life. Simul- 



