NOTES AND MEMORANDA. 337 



cover glass is not put on very quickly the sections may 

 shift or delicate sections come to pieces and float over the 

 slide. It being necessary to use the balsam in such a fluid 

 condition and a certain amount of turpentine always remain- 

 ing upon the slide, the slides should be looked over the 

 next day and more balsam added at the edge of the cover 

 glass if necessary. 



These methods, especially that of fastening the sections to 

 the slide with shellac, although suggested and elaborated by 

 zoologists for the purpose of mounting serial preparations, 

 will, no doubt, come into very general use in ordinary histo- 

 logy for such tissues as placenta or spleen where very thin 

 sections have always been found liable to fall to pieces and 

 the most important pieces to fall out and be lost. 



I have especially to thank the members of the stafl" of the 

 zoological station at Naples for my knowledge of the above 

 process which may, indeed, in its entirety be said to have 

 emanated thence. 



The hardening and staining processes I have described are 

 those I have found to answer best for a large variety of 

 objects, but they can, of course, be modified to suit special 

 cases. — Alfred Gibb Boukne, B.Sc. (Lond.), University 

 Scholar in Zoology and Assistant in the Zoological Labora- 

 tory, University College, London. 



The Central Duct of the Leech's Nephridium. — Since de- 

 scribing the structure of the nephridia in the medicinal 

 leech^ I have devoted a considerable amount of time to the 

 investigation of the comparative histology of the other 

 Hirudinean genera which I have been able to obtain, and 

 have made furtlier observations on Hirudo which have led 

 me to alter my conclusions as to one or two details. 



Both picrocarmine and hsematoxylin failed to thoroughly 

 stain the nephridial cells, but with borax carmine 1 have 

 succeeded in staining the peripheral portion of the cell and 

 the nucleus. 



The use of borax carmine has demonstrated the existence 

 of 7iuclei in the walls of what I have called the central duct, 

 showing the walls of this duct to be cellular and not merely 

 cuticular as I had supposed. 



I am indebted to Dr. Arnold Lang, of the zoological 

 station at Naples, for pointing out to me that in Aulostomum 

 the walls of this duct are formed of cells which, although 

 in rather a degenerate condition, are easily seen. 

 ^ This Journal, vol. xx. July, 1880. 



