The Cutaneous Glands of Common Toads. 34-3 



who say anything about the distribution of the so-called poison gland, 

 say, that thoy are fouiul only in the dorsal skin. The mature glands 

 "wherever occurring in the toad presents the same epithelium and 

 muscle structure, but they vary greatly in size according to their 

 location. With the variation in size, the neck, collar and acinus 

 change proportionately. The largest glands are found in the central 

 areas of the parotids. As many as 130 large sacs have been counted 

 in one parotid. About the edges of these warts the glands are smaller 

 and may be very irregular in shape (Fig. 14). In all other warts 

 the glands are smaller and fewer in number, but they bear to each 

 other a similar relation as in the parotids (Figs. 21). The smallest 

 mature glands occur singly and only occasionally in the ordinary 

 skin of the back, and in the ventral skin. The effect of pressure from 

 adjacent glands is here eliminated and the acinus tends to assume 

 a shape more nearly spherical, seldom larger than 175 microns in 

 diameter. Those glands that are somewhat compressed at the poles 

 range in depth from 175 to 290 microns and in transverse diameter 

 from 280 to 360 microns. 



Expulsion of the secretion. I have for several reasons spoken 

 of the above as the mature glands. They contain the secretion in 

 its final form, i. e., a finely punctuated liquid in which float count- 

 less poison grains,. The nuclei may continue to produce secretion 

 and the lumen of such a gland acts as a reservoir for the secretion 

 until needed by the animal for its protection. Bristol and Bartelmez, 

 who have recently stated that there are both mucus and poison glands 

 in the toad, say that "when a poison gland has reached its full 

 development, it is simply a reservoir of poison." I have not been able 

 to learn if all or only a part of the mature glands are discharged 

 as the result of a natural stimulus. The results of artificial stimuli 

 differ. Electricity applied to a limited area of the skin causes a 

 flow of secretion from that part alone. The same is true of mechanical 

 stimulus. Pithing the animal in no case caused a discharge, but 

 decapitation or killing with chloroform, in many instances, produced 

 a general expulsion of secretion. 



Authors have quite generally agreed that the expulsion of the secre- 

 tion is due to the contraction of the smooth muscles about the gland 



