566 WALLACE. [Vol. VIII. 



upper end. (Fig. Ill, c.) While it is true that ruptured cells 

 are not abundant in sections, this may be owing to the fact 

 that they are much shrunken when emptied of contents and 

 soon cast out, their places being filled by the distension of fresh 

 cells. The great number of shrunken cells in the secretion 

 make this more certain and in many cases they have been found 

 in sections closely pressed between the rapidly filling fresh 

 cells. The bursting of the cell seems to be a simple mechanical 

 necessity, though why it should always occur at the upper end 

 of the cell is not so clear, unless it be that this point alone is 

 free, the delicate superficial layer offering little resistance. 



A few points in the development of the axillary gland were 

 studied, and it was found to make its first appearance in larvae 

 about two-fifths of an inch in length, originating as a simple, 

 epidermal thickening which sinks below the surface as an open 

 pit. A little later the lining of the pit becomes differentiated 

 into the cells shown in Fig. II. In larvae four-fifths of an 

 inch in length, the mucous cells, which take their origin from 

 the polygonal cells in which they lie embedded, are already 

 active, while the clavate cells, still immature, are seen to be 

 merely elongated cells which have grown and taken on the 

 character of a secreting cell, the protoplasm being crowded 

 to the wall to make room for the fluid which it secretes. 

 (Fig. IV.) In Fig. V, representing a longitudinal section of 

 the gland taken from a fish three inches long, the simple pit 

 has begun to be thrown into folds, this process continuing 

 with the multiplication of cells until we have the more com- 

 plex structure of the adult shown in cross section in Fig. VI. 



Some other structures on different parts of the body seem 

 to bear such a close relation to the axillary gland that they 

 must not be passed by without a word. One of the peculiar- 

 ities of the operculum is that it lies close to the body-wall 

 excepting at the upper point of attachment where it hangs 

 out, making a large, foramen-like opening for the passage of 

 water. Underneath this free border of the operculum, and 

 near the base of the pectoral fin, is a patch of glands identical 

 in structure with the one described above, but the clavate cells 

 are larger and the whole structure is well developed at a time 



