276 IlJ'nioh Sftife Tuilmrdtorii of Nntiiyal TTistory. 



discussion was found. Wills ('80) found that the daughter 

 colonies of Volvox glohator escaped through a rift in the pos- 

 terior hemisphere of the parent, and Klein ('89) observed the 

 same phenomenon in Volvox aiirciis. The escape of the 

 daughter colonies in Plcodorina has not been observed l)y 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 centers 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 ('86) in I'diidoriiKi, but iodine or methylen 

 blue demonstrates a finely granular condition like that 

 described for Eudorina. The sheath is traversed by the pairs 

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



The matrix (/».) is a gelatinous substance of some consist- 

 ency, 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 

 condition found in the maternal colonies, is shown by the 

 fact that the flagella of the young forms, before rotation 

 begins, can be seen to penetrate the matrix of the parent very 

 slowly. Their ends are often bhmted or even knob-like and 

 their lateral motion is very limited. The movement of the 

 young colonies through the matrix is a very slow and gradual 

 one, showing the gelatinous consistency of the sul)stnnce in 

 which they are imprisoned. 



The striking feature in the strnctiu'e of this species, as in 

 the case of P. (■(dlforn'icn (Shaw, '1)4), is the presence of two 



