92 ATLAS OF BIOLOGY. 



FIG. XVI. Another, after the discharge of the antherozooids. 



(Figs. XV. and XVI. were near the margin of the prothallus. Figs. XIV. to XVI. 

 D. 4.) 



FIG. XVII. Section across the sexually mature prothallus, through the plane a- b, of 



Fig. XIII. 



The left half* of the figure represents three views of the unfertilized archegomum in 

 Aspidium, and the right half corresponding aspects of the antheridium in Pteris. In each 

 case they are 



i. The ripe organ, surface view. 



ii. The same in section. 



iii. The young organ, in section. D. 3. 



No attempt has been made to fill in the detailed structure of individual cells. The 

 archegonia not unfrequently occur on the upper side of the prothallus as well as on the 

 under. 



FIG. XVIII. Three ripe antherozooids, after liberation under pressure. 

 i p.c. osmic acid. Gundlach's ^th immersion. 



FIG. XIX. The segmenting egg-cell of Asplenium. 



After Schenk (139), vol. i., p. '217. 



The first formed septa are indicated by a thick black line. 



FIG. XX. Section across an embryo-bearing prothallus of Nephrolepis, cut as directed 

 for Fig. XVII.* A. 3. 



In Figs. XIX. and XX. homologous parts are shaded alike, and the arrows indicate the 

 directions of growth of the four subdivisions of the embryo. 



* Marks the line of differentiation of the vascular bundle. 



For Pteris, similar stages to the above have been figured by Hoftneister and others. 

 They are reproduced in Luerssen (136), vol. i. 



See also Hofmeister's papers on the higher Cryptogams. Translated by F. Currey. 

 Bay 8oc. Publications, 1862. 



FIG. XXI. A fern-bearing prothallus, seen from beneath, x 8. 



The central dark line indicates the bundle system, and the parts of the embryo are 

 shaded as for Figs. XIX. and XX. 



* For the sections from which these were drawn I am indebted to my friend Mr. F. 0. Bower. 



