megalosphere and the microspheric and megalospheric tests, etc. 93 



The microsphere probably arises as a zygote formed by the 

 conjugation of the zoospores produced by the megalospheric in- 

 dividuals ; and the size of the microsphere is found not to vary 

 outside 15-20 fi in the four species (N. gizehensis, laevigatus, 

 Orbignyi and variolarius) in which it has been measured. 



The two modes of reproduction are thus contrasted in the size 

 of the offspring. 



The great reduction in the size of the megalospheric test in 

 the earlier species on the list (N. complanatus, perforatum, &c.) 

 was compared with the corresponding phenomenon offered by 

 Ferns, in which the prothallus is dwarfed by the large size of 

 the sporophyte. 



