38 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



same report in regard to the early stages of amphibian material and con- 

 clude that the only safe way is to imbed and preserve in paraffin. Much 

 difficulty was encountered at first in cutting tlie younger specimens. 

 The yolk crumbled under the knife and utterly destroyed the tissues. 

 This trouble later disappeared, I believe tlie change in method which 

 brought about the amelioration was a shorter sojourn of the objects in 

 the higher grades of alcohol, xylol, and paraffin. I generally found it 

 sufficient to leave the smaller embryos but five minutes in each of the 

 following : absolute alcohol, xylol, soft paraffin, hard paraffin. A 

 number of stains were tried. I finally restricted myself to Delafield's 

 haeraatoxylin followed by orange G. A weak solution of Delafield's haema- 

 toxylin in water was employed, of such a strength that the nuclei 

 stained to the proper shade in about thirty minutes (staining was always 

 done on the slide). Treated in this way this stain is so selective tliat 

 no decolorizing is necessary. The slides were then washed in tap-water 

 and passed through ascending grades of alcohol, in one of which (prefer- 

 ably 70 per cent) some crystals of orange G had been dissolved. The 

 latter does not overstain the yolk, as most plasma stains do. This pro- 

 cess makes the nuclei blue, in sharp contrast with the orange yolk and 

 paler yellow cytoplasm. In the older stages the cytoplasm usually stains 

 a faint blue. 



In describing the mesonephric development I shall make use of the 

 following terms : blastulae (the *' Blaschen " of German writers), inner 

 tubule (main tubule, canalis principalis), inner funnel, outer tubule or 

 nephrostomal tubule (canalis nephrostomalis), outer funnel or nephro- 

 stome, Malpighian body, and glomerulus. The "visceral layer" of the 

 Malpighian body (Semon) I shall call the glomerular covering, reserving 

 the term '* Bowman's capsule" for the " parietal layer." 



The work was begun and the part relating to Amblystoma practically 

 completed at the Museum of Comparative Zoology of Harvard University 

 at the suggestion and under the direction of Dr. E. L. Mark. It gives 

 me pleasure to express my gratitude to him for his constant aid. I wish 

 also to thank Doctors W. E. Castle and G. H. Parker for their interest 

 and suggestions. The work was completed at the Sheffield Biological 

 Laboratory of Yale University, and I am indebted to Professors S. I. 

 Smith and W. R. Coe of that institution for many favors. 



