MARSILIA VESTITA. I9I 



sperm-cells, or thirty-two in the whole antheridium. The 

 whole division in M. vestita may be completed within 

 about seven hours from the time the spores are placed in 

 water, and the formation of the spermatozoids begins 

 about an hour later and appears to require about four 

 hours for its completion. 



The full-grown prothallium (pi. iii, fig. 20) appears 

 very different when seen from different sides. A median 

 vertical section, passing through both groups of sperm- 

 cells, shows usuallv the small vegetative cell (.v), above 

 this the broad basal cell of the antheridium (;//), and 

 above this the two clearl}- marked oval groups of sperm- 

 cells, sometimes in contact, sometimes separated by a 

 sterile cell, and separated from the outer wall of the an- 

 theridium by the lateral sterile cells (/) and the cover 

 cell (<^). If a vertical section is made at right angles 

 to the one just described, only one of the groups of 

 sperm-cells will be seen, and the lateral peripheral cells 

 appear much broader (pi. iii, fig. 20, b). A cross section 

 of the antheridium shows the two svmmetrical groups of 

 sperm-cells, as shown in fig. 20, c. 



The walls of the sperm-cells are exceedinglv delicate, 

 but perfectly evident, especially when the contents are 

 contracted, a case that happens very frequently, especially 

 after the spermatozoids begin to form. 



In the early stages of the prothallium and antheridium, 

 the nuclei are large and verv distinct but with compara- 

 tively little chromatin, so that although dividing nuclei 

 were often met with, the figures were very small and not 

 easily studied. In the sperm-cells, previous to the forma- 

 tion of the spermatozoids, the nuclei are less readilv 

 seen, owing to the readiness with which the cytoplasm 

 takes up stains, and consequently Marsilia does not afford 

 a very satisfactory subject for the study of the develop- 



