172 CHARLES L. PARMENTER 



The living larvae were thrown into Flemming's stronger solu- 

 tion. After about four hours of fixation, the tails were split 

 dorsoventrally- into two thin plates of cells. These two plates 

 of cells were then fixed twenty hours longer. After washing 

 in running tap-water for twelve hours or more, the pieces were 

 stained in toto in Heidenhain's haematoxylin, carefully dehy- 

 drated, and cleared in xylol and mounted in damar. 



Gill-plate epitheliiim 



The most successful gill-plate preparations were also obtained 

 from larvae f to 1^ inches lolig. In each larva there are eight 

 gill plates, one subtended from each gill arch and another behind 

 each posterior gill cleft. These gill plates contain very numer- 

 ous mitotic figures. They are composed of two epithelial 

 lamellae with connective-tissue cells and capillaries lying between 

 them. The two layers, unseparated, are so thin that they give 

 very excellent preparations. 



The material was fixed in situ by dropping the living larvae 

 into the Flemming's stronger solution as soon as they were taken 

 from the net. They were fixed in situ twenty-four hours and 



2 Haecker ('99) describes a very successful method of separating these two plates 

 of cells. The posterior end of the larva is cut off after fixation just in front of 

 the cloaca. With a sharp scalpel the thick cephalic end of the tail is split dorso- 

 ventrally through the middle of the vertebra to a depth of an eighth of an inch 

 or more. By grasping with the forceps the ends thus made free, the two layers 

 of epithelium can be pulled apart in a manner similar to separating two sheets 

 of fly-paper with adhesive surfaces sticking together. Professor Sigerfoos advises 

 separating the two layers after about four hours of fixation and then allowing to 

 fix about twenty hours longer. 



The numerous large mitotic figures in various stages with clear cell walls 

 which can be studied without an immersion lens makes this material excellent 

 for the class-room. The gill-plate preparations are equal or superior to those 

 of the tail epithelium. Those of larger larvae are too thick when mounted in 

 toto, but give very satisfactory preparations when separated. Peritoneal prepa- 

 rations of larger larvae contain fewer mitoses and the cell walls are indistinct. 

 However, preparations can be made from the more rapidly growing shorter 

 larvae from which the gill-plates were taken and would probably contain more 

 divisions. Preparations of Ambystoma punctatum are less favorable than those 

 of A. tigrinum because there are fewer figures, more pigment cells in the tail 

 epithelium and the gill-plates are small and thicker. 



