DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 921 



should have an origin so different in the higher animals. However, the condition of 

 that organ in the sturgeon, tunny, and other forms would lend colour to such a view, 

 even with the knowledge of the special rudiment in such forms as Salmo, Perca, and 

 Platessa. 



Towards the end of February, and later, many of the larval wolf-fishes showed a 

 whitish streak in the interior of the intestine. It was uniformly opaque white, and 

 apparently consisted of nutrient matter. In section this mass presented a series of 

 peculiar crystalline and probably fatty bodies. 



The changes which take place in the structure of the digestive tract in Anarrhichas 

 are noteworthy, and consist chiefly of the differentiation of the elements of the mucous 

 lining, the increase of the circular and longitudinal muscular fibres, and the greater 

 complexity of the folds of the walls, chiefly internally, but also externally. In the stage 

 just described (17th January) the stomachal part of the canal has attained little develop- 

 ment, and its mucous coat shows only a few frills of finely granular epithelium. As 

 development proceeds, however, the oesophageal region of the canal is thrown into a 

 complex series of frills, and the mucous lining is supplied with large globular glands. 

 In the oldest stage (20th June) the folds of the oesophageal region are more complex 

 than in the earlier stages, many of them being subdivided, and the longitudinal fibres 

 (inside the circular) are more distinct dorsally and ventrally. The glands are arranged 

 as a close and somewhat regular series of globular bodies along the inner surface of the 

 folds (PI. XXVII. fig. 5). Proceeding backward the complexity of the folds increases, 

 while the canal becomes rounder, the lamellae being pinnate in transverse section, from 

 the number of the secondary folds. The globular glands now cease in the walls of the 

 folded ridges, and an alteration occurs in the appearance of the latter, which assume a more 

 or less circular condition in section, and in their wide bases are a series of large circular 

 areolae,* probably glandular (dre, PI. XXVII. fig. 4), the inner wall of the gut over 

 these being composed of closely-set cylindrical epithelial cells. These globular spaces 

 also occur under the wall, where there are no lamellae. The calibre of the canal 

 becomes smaller and the lamellae thicker, a few secondary processes or folds appear- 

 ing on their surface. The latter has fine columnar epithelium, and the sub- 

 mucous tissue is composed of granular glands, probably modifications of the large areolae 

 in front. These lamellae become more distinctly pinnate before ceasing at the pylorus. 

 The wall of the canal is highly muscular, the fibres forming a complexly interwoven layer 

 externally. The next region of the canal to be distinguished is that behind the valvular 

 folds of the former, and it is characterised by its thinner muscular walls, and the change 

 in its glandular lining, for the numerous simple folds around its walls have coarser and 

 more lax epithelium than the foregoing. Externally is a peritoneal investment (with 

 probably a few muscular fibres), then longitudinal fibres grasped between the outer and 

 the next layer, with, finally, an internal circular layer of fibres. 



Posteriorly, the gut diminishes in calibre, and by and by the folds chiefly affect the 



* These areolae in the sketch are perhaps too conspicuously cellular. 

 VOL. XXXV. PART III. (NO. 19). 7 B 



