ANCYLISTALES 121 



swarmspores. Sporangia and sexual cells are formed in the same 

 or different thalli. The germinating sporangium puts out a 

 slender exit tube as in Achlyogeton, but here a thin-walled vesicle 

 rounds up at the tip of the tube and the contents of the spor- 

 angium pass into it. In M. prolifemni Schenk (Fig. 44, h) the 

 process of swarmspore delimitation is completed in the vesicle, 

 the swarmspores being no more than imperfectly fashioned 

 when the protoplasm flows through the tube. In M. vermicolum 

 (Zopf) Fischer (Fig. 44, d), the swarmspores are fully formed in 

 the sporangium, and the vesicle may rupture before all of the 

 swarmspores have passed into it (Dangeard, 1906: 'pl. 3). In 

 any case there is no Achlya-MkQ encystment comparable to that 

 occurring in Achlyogeton. 



The cells of the thallus which function as sporangia are globose, 

 ellipsoidal, or irregularly contoured. Rarely two exit tubes 

 occur. The swarmspores are laterally biciliate, the cilium which 

 trails in swimming being longer than that which precedes the 

 spore. The gametangia resemble the sporangia in shape, the 

 male cell being commonly the more slender. 



Knowledge of nuclear phenomena in the genus rests on the 

 work of Dangeard (1906) on M. vermicolum Zopf. Numerous 

 nuclei lie scattered through the young thallus. Each sporangium 

 receives several nuclei when segmentation of the thallus occurs, 

 and subsequently these divide repeatedly to provide the nuclei 

 for the uninucleate swarmspores. In those cells of the thallus 

 which are to function as gametangia a relatively small number 

 of nuclei exist. The male gametangium (" antheridum ") usually 

 contains two nuclei, while the female gametangium ("oogonium ") 

 contains approximately eight. Later all but one of the female 

 nuclei disintegrate and disappear. One male nucleus enters 

 the female gametangium, while the other usually fails to function. 

 In cases in which the male cell is intercalary between two female 

 cells it is possible that the two male nuclei fertihze different 

 female cells. A coenocentrum was not demonstrated. The 

 sexual nuclei fuse in the young resting spore. After hibernation 

 the fusion nucleus divides, about ten nuclei being provided for 

 the swarmspores. 



The genus was founded on M. proliferum Schenk, occurring in 

 the c ells of varous green algae {Oedogonium, Cladophora, Zygnema, 

 Spirogyra, Mesocarpiis, Mougeotia). This species is widely 

 distributed in Europe and has been collected in America (Martin 



