The Cutaneous Glands of Common Toads. 349 



of Amiurus, mucus cells which produce the slime that covers the 

 surface of the skin. These cells, he says, are common to all Pisces. 

 Each is a one-celled gland, which, when fully grown, opens to the 

 surface and may measure from 20 to 25 microns in length. 



Ayres ('93) has described for Bdellostoma dombeyi, a row of 

 thread glands whose pores open on either side of the body. These 

 glands produce grains which, when poured into the water, unroll and 

 an enormous transparent gelatinous mass is formed about the animal 

 for its protection. This acts merely in a mechanical way. These 

 glands are sunken in the muscles of the body. He does not say if 

 one-celled glands are present generally in the epidermis. 



Maurer ('95) figures single mucus cells in the epidermis of Bdel- 

 lositoma. He also figures such glands for many higher fishes, in- 

 cluding the eel, and also for the larvae of Batrachians. 



We have earlier seen that the only one-celled glands in the epi- 

 dermis of the adult toad are the beaker cells, which open below the 

 molt and not to the surface. All the cutaneous glands are, however, 

 in connection with the epidermis from which they arose. The smaller 

 of these have frequently been called mucus glands in contrast to the 

 larger ones which have been called the poison glands. But we know 

 that the adult toad differs from fishes and certain Batrachians in that 

 it is not adapted to permanent water conditions. Each year, during 

 the breeding season, the adult toad spends but a day or two in the 

 water. For this, the toad requires no more of an adaptation to the 

 water than does the mammal, for example, which occasionally swims 

 in the water. The adult toad is adapted to a drier environment than 

 any other Batrachians of a similar distribution. It is highly im- 

 probable, then, that in the adult toad, whose skin is normally dry, 

 the large number of small glands, with numerous secreting cells, 

 should function solely in the production of mucus. 



We have seen that a reticular mass is sometimes present in the 

 lumen of the smaller glands (Eigs, 29, 33). Others, especially the 

 transitional glands, may contain in the lumen a homogeneous or 

 slightly granular secretion (Fig. 40). In the outer part and about 

 the periphery of the acinus of the mature glands, either a homo- 

 geneous or finely punctuated secretion is occasionally present (Figs. 



