No. 3-] AXILLARY GLAND OF BATRACHUS 567 



when the former is at an early stage of development (Fig. VII). 

 The glandular patch is perforated by numerous foramina, each 

 opening into a separate chamber or invagination homologous 

 with those of the axillary gland, so that if the opercular 

 glands were depressed and had a common opening we would 

 have a many-chambered axillary sac. It is possible that the 

 pouch-shape of the latter is due to its position in the axil of 

 the fin. On the under side of the pectoral fin, and following 

 the general course of the rays, is a third set of similar glands 

 and yet no connection between the three has been traced. 

 Their relative position is shown by dotted lines in Fig. VIII. 



Sections of the skin in different parts of the body prove it 

 to be of essentially the same structure as the glands, the cells 

 having a similar origin and apparently a similar method of 

 emptying secretions. The large cell which corresponds to 

 the clavate is rounded, 70 /a in diameter, and it also pushes 

 a projection through the superficial layer of the epidermis, 

 emptying the contents on the surface. (Fig. IX.) The slime 

 found in abundance over the whole body of the fish contains 

 quantities of large, empty, rounded cells just as the secretion 

 in the gland contains the empty flask-shaped cells, and secre- 

 tion of the glands or of the skin turns blue litmus-paper red. 



It is a significant fact that the three different sets of glands 

 are all found in the region of the pectoral fin, though just what 

 part they play in the life of the animal is an obscure point. 

 The structure of the gland, the want of any close connection 

 with the spines, and the results gained from a few simple 

 experiments made with the living fish, do not seem to favor 

 the idea of a poisonous secretion. My work, however, has 

 not been sufficient to determine the nature of the secretion 

 which still offers an interesting problem to the physiologist. 



Marine Biological Laboratory, 

 Woods Holl, Mass., Aug., 1892. 



