196 CALIFORNIA ACADEMY OF SCIENCES. 



but not always, the first wall cuts off the papilla at the 

 top of the spore from the cavity below (pi. iv, fig. 5). 

 The nuclei of the two cells are ver}^ unequal in size, the 

 lower one being much smaller. Both are strongly flat- 

 tened and the division wall is very convex, and a small 

 part of the fine granular protoplasm of the papilla is usually 

 cut off from below and remains in the lower cells. The 

 lower large cell takes no further part in the formation of 

 prothallium and remains with very httle change until after 

 the fertilization of the archegonium. 



The next division in the upper cell is usually a nearly 

 vertical wall which cuts off 'c\ small peripheral wall (pi. 

 Wy figs. 6 and 7). and this is followed later by usuall}^ two 

 similar ones (fig. 10. ii and iii), which, with the first 

 formed enclose a large central cell, the mother-cell of the 

 archegonium. On comparing this stage with the same 

 one in Pilularia, we find that in the latter the periph- 

 eral cells are not formed until a second wall, parallel to 

 the basal wall is formed, and, as a rule, but two walls are 

 formed instead of three in the cutting off of the arche- 

 gonium mother-cell. That this difference is not essen- 

 tial, however, is seen from the fact that occasionally in 

 Marsilia the basal cell is formed before the peripheral 

 cells are all cut off (pi. iv, fig. 9). 



A variation occasionally met with was the cutting off 

 of a lateral cell before the separation of the prothallium 

 from the body of the spore. 



Generally, before the second peripheral is cut off, the 

 first formed one has already divided by a vertical wall 

 into two small parts (pi. iv, fig. 7). At this stage the 

 prothallium, exclusive of the body of the spore, consists 

 of a large central cell, the mother-cell of the arche- 

 gonium (fig. 10. o) , and three peripheral cells (p) which 

 have undero-one more or less further division. The 



