98 AQUATIC PHYCOMYCETES 



The nucleolus is variable in appearance and possibly changes in shape 

 during prophase; it ultimately becomes a ring-shaped structure. Nu- 

 clear division is mitotic and synchronous, and the division spindle is 

 intranuclear (Fig. 8 G). In the equatorial-plate stage it is narrow and 

 spindle-shaped, with its poles terminating in minute dense bodies from 

 which faint cytoplasmic strands radiate. The chromosomes are not 

 clearly distinguishable as discrete bodies, but, rather, form a crowded 

 nodular band across the equator. The nucleolus persists during divi- 

 sion, lying very close to the equatorial band of chromosomes but sep- 

 arate from them. The resting spore is uninucleate and, upon germi- 

 nation, functions as a prosporangium — no cytological information 

 is available on this phase. 



With respect to the operculate monocentric chytrids, the data at 

 hand come chiefly from Hanson's (1946a) work on the apophysate 

 epibiotic species Catenochytridium laterale (p. 558). In this form, be- 

 cause of the strongly developed endobiotic apophysis, the secondary 

 apophyses, and the catenulations on the rhizoidal system, as well as 

 the "endo-exogeneous" method of development, the nuclear condition 

 of the thallus is of unusual interest (Fig. 8 A-E, p. 97). In the case 

 of Chytridium lagenaria, Karling (1936a) earlier had postulated that 

 the original zoospore nucleus might migrate into the developing endo- 

 biotic apophysis, there to multiply during endogenous growth, and, 

 further, that the resulting daughter nuclei then passed out with the 

 protoplasm, during the exogenous growth of the zoospore cyst, into 

 the mature sporangium. According to Hanson, Catenochytridium 

 laterale and C. carolinianum have types of development similar to 

 Chytridium lagenaria. She says that the nucleus in both Catenochytri- 

 dium laterale and C. carolinianum remains in the extramatrical zoospore 

 cyst during the development and maturation of the rhizoidal system 

 and apophysis (Fig. 8 A-B). With zoosporangial development in both 

 species the nucleus increases in size and, while the incipient zoospo- 

 rangia enlarge, the primary nuclei divide. Nuclear division in both 

 forms is mitotic, intranuclear, and synchronous. At metaphase, the 

 nucleolus of Catenochytridium laterale is very prominent (Fig. 8 D), 

 but that of C. carolinianum is either lacking or reduced. Further ob- 

 servations are essential before it can be established whether the nucleo- 



