142 Dr. C. A. Kofoid on Pleodorina illinoisensis. 



one (iJ.), which shows no traces of the concentric structure 

 found in Pandorina. It is within this latter layer that the 

 increase in thickness takes place in the older colonies. It is 

 limited centrally by a thinner and less highly refractive 

 layer (m.m.), which encloses the common matrix (m.) in which 

 the cells of the colony lie. Frequently among the older 

 organisms there occur upon the posterior end of the colonies 

 blunt pseudopodia-like protuberances (PI. V. fig. 4) of the 

 sheath, of irregular form and of no constant number. Their 

 position and the fact that they are often, though not always, 

 found in old colonies from which some of the daughter colonies 

 have already apparently escaped, suggest that they may mark 

 the place of exit of the young individuals from the parent. 

 Similar protuberances were observed upon Eudorina and 

 Pandorina, under similar conditions, in the collections in which 

 the Pleodorina under discussion was found. Wills (1880) 

 found that the daughter colonies of Volvox globator escaped 

 through a rift in the posterior hemisphere of the parent, and 

 Klein (1889) observed the same phenomenon in Volvox aureus. 

 The escape of the daughter colonies in Pleodorina has not 

 been observed by me. 



The sheath stains deeply in an aqueous solution of methylen 

 blue, more deeply, in fact, than the enclosed matrix, the outer 

 layer taking the deeper stain. It also shrinks to about one 

 fourth its former thickness. This shrinkage, together with 

 that of the central matrix, causes the sheath to wrinkle along 

 lines which bound hexagonal areas from whose centres the 

 cells now project, thus giving the appearance of a division of 

 the surface of the colony into regular polygons. The sheath 

 shows no trace of the layer of radial rod-like structures 

 found by Klebs (1886) in Pandorina, but iodine or methylen 

 blue demonstrates a finely granular condition like that 

 described for Eudorina. The sheath is traversed by the pairs 

 of flagella which arise from the outer ends of each of the cells. 



The matrix (w.) is a gelatinous substance of some con- 

 sistency, filling the colony inside of the inner membrane. In 

 the living colonies, in those which were killed in the various 

 reagents mentioned above and afterwards stained, and in 

 disintegrating material, no traces of any divisions can be 

 detected in this substance that are not due to wrinkling caused 

 by shrinkage. Methylen blue or iodine causes the matrix to 

 show a faintly reticulated or vacuolated appearance due to 

 different densities of staining. That the substance of the 

 matrix has considerable consistency, even in the swollen con- 

 dition found in the maternal colonies, is shown by the fact 

 that the flagella of the young forms, before rotation begins, 



