1914] Kofoid: Phytomonila regularis 37 



daughter quartets into an intercalated peripheral row. while the two 

 distal polar daughter quartets remain in an axial position with the 

 inner end of each in contact with that of a cell of the quartet of the 

 opposite pole. 



The process of development of the coenobium unfortunately has 

 not been observed, but there is some evidence in the mutual adjustment 

 of the cells, as observed, which is confirmatory of the conception of 

 the derivation sugg&sted. In the first place, the cells of the peripheral 

 row can be plainly separated into two quartets whose cells alternate 

 in po.sition and lie at slightly different levels, as indicated in the 

 diagram (fig. 46, and. seen in a lateral \new. fig. 3). One quartet is 

 at a slightly higher level (viewed from the apex) than the other. In 

 a similar way, as before noted, two of the cells of each polar quartet 

 are at a higher level than the others and come more nearly into 

 apposition in an apical cross-line. It seems probable that the members 

 of the apical quartets are sister cells respectively of the cells of the 

 quartet of the peripheral ring which are nearest them, i.e., are at the 

 higher level as seen from the pole in question. This relationship is 

 indicated in the dia^am (fig. 4) by the connecting arrows. 



This simple organism with the elemental geometrical relations of its 

 constituent cells affords a unique species for an analysis of the play 

 of mechanical forces and their integration in the formation of the 

 lenticular colony. The adhesion of the quartets of the eight-cell stage 

 by their equatorial ends in the plane of the equator and the consequent 

 crowding to the periphery of the proximal sister cell upon their 

 di\nsion would afford an immediate basis for the formation of the 

 lenticular colony of the type here obsers-ed. The lack of develop- 

 mental stages precludes for the present any further consideration of 

 this phase of the subject. 



The cells of the coenobium are .subequal. those of the apical quartets 

 being .somewhat flatter distally and more squarish than thase of the 

 peripheral ring, which have a broadly rounded exposure and with 

 opposite in.stead of contiguous faces flattened. Each of the cells bears 

 upon its exposed surface a centrally located, slightly squarish area 

 which is the least bit elevated. This is delimited by a minute depres- 

 sion in the surface which involves the cell- wall and .slightly indents the 

 protoplasm below and is best seen in optical section. There are no 

 proces-ses on this area, and it is detected only by close scrutiny and is 

 with difficulty demonstrable upon the surface of the apical cells. It 

 is presumably homologous with the more pronounced elevations or 



