THE PYGIDLUM OF THE COMMON FLEA. 227 



nuclei, which pass over, at a later stage, into the fertilising tube of 

 the antheridium, but whether they pass into the oospore is a ques- 

 tion which has not yet been settled. 



[An interesting, illustrated account of " Cystopus, or White 

 Rust," was given in the Journal of Microscopy and Natural Science 

 for June, 1885.— G. H. Bryan.] 



^bc ip^tjiMum ot the Common jflea** 



By Dr. Alfred C. Stokes. 



THIS organ has been studied so frequently, and by so many 

 microscopists ; it has been used for so many years as a 

 test of certain qualities in objectives, that further notes on 

 the subject might be deemed superfluous; it might well be thought 

 that the last word must have been spoken about a matter so com- 

 mon, not to say so hackneyed. It is because the pygidium has 

 been so frequently examined that I cannot divest myself of the 

 belief that the structural features which I have recently observed 

 must have been repeatedly seen by microscopists, although these 

 morphological points seem to be actually undescribed. I can find 

 no reference to them in the literature of the subject which I have 

 been able to examine, yet they are so prominent and so conspic- 

 uous that it is difficult to imagine how they could have been so 

 long overlooked, if they have been, especially after such accom- 

 plished microscopical observers as Van Heurck, Dallinger, Nelson, 

 Carpenter, have used the pygidium as a test. But some of these 

 investigators, notably Dallinger and Nelson, have lately described 

 previously unobserved features, or features which have previously 

 been misinterpreted. 



Mr. E. M. Nelson was the first to describe correctly the form 

 of the so-called spines or hairs which clothe the inter-areolar sur- 

 face, calling them lambent, meaning that they are flame-shaped, 

 thus using the word out of its proper signification, for "lambent" 

 means, not flame-shaped, as the eminent British microscopist 



* From The Journal of the New York Micro. Soc. 



