96 AQUATIC PHYCOMYCETES 



the sporangium becomes multinucleate. Subsequently, uninucleate seg- 

 ments are progressively cleaved out of the protoplasm. 



In addition to that on Aster ophlyctis some fragmentary cytological 

 data on a few other inoperculate monocentric chytrids are available. 

 Hanson (1944a) found in Loborhiza metzneri (see p. 227), a parasite 

 of Volvox, that the nucleus of the epibiotic infecting spore migrates 

 late from its cyst into the developing endobiotic sporangium. She gives 

 no details but, from her figures, the nucleus then apparently multiplies 

 while the rudimentary sporangium is still somewhat cylindrical and 

 unexpanded. Sexual reproduction is by conjugation of an immature 

 receptive thallus and a swarmer which comes to rest upon it. The two 

 nuclei can be clearly followed during the development which ensues, 

 and the resting spore near maturity bears a single, presumably fusion, 

 nucleus. 



Hanson (1946b) also discusses certain details of the cytology of 

 Phlyctorhiza endogena (see p. 392). In this inhabitant of the basement 

 membrane of mosquito integuments, the rudiment of the sporangium 

 remains uninucleate until fairly well developed, but as it enlarges the 

 nucleus also increases in size and soon multiplies. Rarely, when the 

 sporangium approaches maturity, may secondary vesiculations of the 

 rhizoids produce new centers of reproduction, into which, it is believed, 

 nuclei migrate from the main body. 



Karling (1946d) figured, but did not describe, some cytological as- 

 pects of Rhizophydium keratinophilum (p. 265). Here, the immature 

 sporangium is uninucleate with the nucleus located, as in other mono- 

 centric chytrids, in the developing reproductive rudiment. When ma- 

 ture size is attained, the nucleus appears to undergo a series of syn- 

 chronous intranuclear divisions, with the daughter nuclei decreasing 

 in size, as in Aster ophlyctis. For the most part, the resting spores are 

 binucleate, which suggests that they may be gametic in origin and dika- 

 ryotic. Occasional ones have more than two nuclei. 



The cytological development of Rhizophydium coronum (p. 251) was 

 followed by Hanson (1945b). The young incipient sporangium is uni- 

 nucleate (Fig. 8 F) and usually remains so until the sporangium 

 reaches maximum size. As the reproductive rudiment grows, its nucleus 

 nearly doubles in size. Densely staining granules occur not only on 



