230 University of California Publications. [zoologt 



Van Gieson's haemalum and picro-fuchsin, and the iron-haema- 

 toxylins of Benda and Heidenhain. I have found it of consider- 

 able advantage to increase the percentage of fuehsin in Mallory's 

 stain to as much as l.."i or 2%. This stain, as a whole, when 

 successful is very beautiful, but its action varies most unac- 

 countably. The staining and differentiation will be perfect in 

 sonic sections, while in others on the same slide the differential 

 coloration will fail completely. But the range of application of 

 the stain seems to be almost unlimited except for purely cytolog- 

 ical work. 



Other stains have been used, such as Mayer's neutral and 

 acid haemal urns followed by eosin, orange <;. erythrosin and 

 Congo red; safranin alone or in combination with light green; 

 ferric chloride haematoxylin, and such special stains as the 

 phosphotungstic acid haematoxylin of Mallory and Cajal's ('03) 

 silver nitrate-pyrogallic acid method for nerves, Tanzer's orcein 

 for elastic fibres, and Mayer's muci-carmine as a mucus stain. 



As has been said, the largest poison glands of Plethodon are 

 situated on the hack of the tail, andin cross sections (PI. XX. 

 Fig. 1, p.gl.) it may he seen that they lie in that portion of the 

 skin covering the dorsal half of the tail. Here the greatest 

 development is in the glands at either side of the mid-dorsal 

 line, while farther down on the sides they gradually diminish 

 until they .ire considerably smaller and not readily distinguished 

 by their size from the larger mucous glands. (PI. XX, Pig. 1. 

 m.gl.) The coloration also of the tail gives a clue to the loca- 

 tion of the largest glands. The dorsal half of the tail is black 

 or In-own. while the ventral half is orange or yellow, and the 

 glands under consideration are confined almost entirely to the 

 darker portion. The mucus glands are found largely on the 

 ventral side of the tail, but they also occur along the dorsal sur- 

 face. In this region they lie between the necks of the large glands. 



The poison glands form large sacs, extending from the epi- 

 dermis to the inner layer of the eorium. (PI. XX, Fig. 1.) In 

 shape they are elongated, with oval or even somewhat rectangu- 

 lar outline. The duets are short, and the transition from the 

 body of the gland to the neck and duct is not sharp as in the 

 mucous glands, which are regularly flask-shaped. 



