March 20, 1908] 



SCIENCE 



455 



lined by a single layer of cubical cells 

 whose distal ends terminate in an indefi- 

 nite boundary between the substance of 

 the cell and the mass of secretion that fills 

 the lumen of the tubule. 



But the secretion mass is not discharged 

 into the water from these tubules. They 

 open into a flat cavity, with enclosed sides, 

 of the single ( 1 ) original invagination by 

 which the gland was formed (presuming on 

 the unknown embryology), and it is this 

 thin outer layer of integument that con- 

 tains the heavy blood supply. 



Another system of capillaries is found 

 between the tubules, and is evidently de- 

 signed to bring a supply of food material 

 within reach of the secreting cells, which 

 are very active as measured by the amount 

 of highly specialized product they secrete. 

 The operation of the organ would appear 

 to be as follows: 



The secreting cells discharge the elabo- 

 rated material (which is a " leucif erase " ) 

 into the lumen of the tubular gland, which 

 carries it up and passes it out into the 

 outer flat spaces in contact with the inner 

 side of the external integument. Here it 

 is used, being consumed by the oxygen 

 that is brought to it in the heavy blood 

 supply of this integument. Its waste 

 products of combustion must also be 

 carried away by this blood and are prob- 

 ably extracted by the kidneys, along with 

 the waste matter from the other body 

 tissues. 



Since the whole structure was probably 

 derived from the stratified epithelium of 

 the outer body surface, the secreting 

 epithelium must be looked upon as the 

 specialized basal layer of this invaginated 

 region. 



The whole gland lies on a layer of con- 

 nective tissue which is modified to reflect 

 light. This reflector is very efScient and 

 when a mounted section is laid on a piece 

 of black velvet, it alone shines out as a 



white line. Still outside of the reflector is 

 found a layer of intensly black pigment. 

 At its upper edge, this is useful in pi'oteet- 

 ing the eye from the organ's light. 



The thickened edge of the lower "lid" 

 consists of an integument covering a mass 

 of cells which appear to be nerve cells. 

 This is probably some ganglion which is 

 used to control the production of light. 

 The Poison Glands of Bufo agtia: C. L. 



Bristol and G. W. Baetelmez. 



The material was collected in Bermuda 

 at the New York University Biological 

 Station, the original habitat being South 

 America. This toad has had the reputa- 

 tion of being poisonous to mammals, and 

 we finally verified instances of poisoning. 

 The poison acts only on a mucous mem- 

 brane, and produces results similar to 

 curari. 



The poison glands are found only on the 

 upper surface of the body, while mucus 

 glands are found all over the skin, and are 

 crowded together in large parotoid 

 ' ' glands" behind each ear. They are much 

 larger than the mucus glands and extend 

 deep down into the compact corium layer. 

 They are surrounded by a thin layer of 

 loose connective tissue which contains 

 nerve fibers and a dense network of capil- 

 laries. There is an almost continuous 

 layer of smooth muscle fibers about the 

 gland. The cells of the glandular epithe- 

 lium develop to an enormous size, and when 

 they mature they disintegrate, their entire 

 plasm becoming the secretion, so that when 

 a poison gland has reached its full develop- 

 ment it is simply a reservoir of poison. 

 When the poison is discharged the remains 

 of the gland are resorbed, and at the same 

 time one of the five or six undeveloped 

 glands, grouped around the mouth of the 

 functioning gland grows down alongside 

 the remains of the discharged gland, push- 

 ing it aside to occupy its former place. 

 {To be concluded] 



