Allen. — The Spermatogenesis of Poly trie hum juniperinum . 289 
by something like a distinct membrane ; but in fixed material no trace of 
such a membrane is to be found at this time, although a similar structure 
does seem to be present in preparations of some antheridia at an earlier 
stage. The separate vesicles are embedded in a viscous substance which is 
probably derived from the material of the broken-down walls. 
A part of the work upon which the present paper is based was carried on 
in the laboratory of Professor Mangin at the Museum d’histoire naturelle, 
Paris. It is a pleasure to record here my appreciation of the unfailing 
courtesy of M. Mangin and his assistants, and of the generosity with which 
the facilities of the laboratory were placed at my disposal. 
The University of Wisconsin. 
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