454 '^^^ AMERICAN NATURALIST. [Vol. XXXVIII. 



smaller bodies as during spore formation among the Myxomy- 

 cetes and Mucorales. Very complete studies have been made of 

 these conditions by Harper, '99 and :00 a. In the slime mould 

 (Fuligo) cleavage begins by furrows on the external surface 

 which " cut down at all angles into the homogeneous proto- 

 plasm." The direction of the cleavage furrows is further com- 

 plicated by the fact that many of them start from the bottom 

 and sides of deep folds. All of the furrows may bend and 

 secondary cleavage planes strike off from them which in time 

 unite with one another until the protoplasm is divided progres- 

 sively into very many small masses (see Fig. 8 b') that finally 

 round themselves off and secrete walls, becoming spores, some- 

 times with one nucleus and sometimes with several. 



Cleavage in the sporangium of Synchytrium and the moulds, 

 as described by Harper, '99, is in general similar to that in the 

 Plasmodium with, however, the additional feature that lines or 

 planes of vacuoles are often utilized to assist a cleavage furrow 

 in effecting the segmentation of the protoplasm. The separa- 

 tion of the spore plasm of the sporangium of Pilobolus from the 

 filament below begins with a cleavage furrow from the exterior ; 

 but this furrow follows and makes use of a curved plane of 

 flattened vacuoles with the result that a dome shaped cleft is 

 developed and two plasma membranes are presented face to face, 

 which form the columella wall between them. The segmenta- 

 tion of the spore plasm in Pilobolus is affected somewhat 

 similarly through the cooperation of cleavage furrows from 

 the exterior with vacuoles which cut into the protoplasm at 

 various angles to meet one another and the cleavage furrows. 

 The bodies first formed in the sporangium of Pilobolus are not 

 the final spores. Harper suggests that they may correspond to 

 the zoospores of Saprolegnia. They are generally uninucleate 

 and begin immediately a period of growth within the sporangium 

 characterized by extensive nuclear multiplication and several 

 divisions of the protoplasmic body by constriction. 



Harper finds that the spore plasm of Sporodinia is separated 

 from the filament below by a dome-shaped plane of flattened 

 vacuoles which fuse together and, unlike Pilobolus, cut their way 

 to the surface of the sporangium. Thus the cleavage is deter- 



