440 
Wilson.—Sex Determination in Mnium hornum. 
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EXPLANATION OF PLATE XX. 
Illustrating Dr. Wilson’s paper on Sex Determination in Mniwn hornum. 
All the figures were drawn with the camera lucida, Figs. 1-4 under a 2 mm. apochr. horn. imm. 
Zeiss N. A. 1*40 with comp. oc. 4, X 500; Fig. 5 under a D achrom. Zeiss with comp. oc. 4, 
x 220 ; Figs. 6, 7, and 8 under a 2 mm. apochr. horn. imm. Zeiss N. A. 1*40 with comp. oc. 18, 
x 2250. 
All the figures refer to Mnium hornum. 
Fig. 1. A young modified archegonium, showing division of the neck canal-cells. 
Fig. 2. A mature modified archegonium in which the contents of the neck have been ejected; 
the naked cells in the venter are probably the ovum and ventral canal-cell. 
Fig. 3. A modified archegonium, showing spermatogenic cells (?) in the neck-canal. 
Fig. 4. A modified archegonium, showing spermatogenic cells (?) in the neck-canal. 
Fig. 5. A bisexual organ, showing spermatids in the upper part and an ovum(?) and ventral 
canal-cell (?) in the lower part. 
Figs. 6-8. Spermatogenic cells from a normal antheridium in late prophase of division, each 
showing six chromosomes. A chloroplast is seen in the right-hand lower corner of the cell shown 
in Fig. 8. 
