MORPHOLOGY AND TAXONOMY OF MASTWOPHORA 283 



plexity culminating in the genus Volvox. Spundyloinonnn is a loose 

 aggregate of 1() cells without gelatinous matrix. These have 4 

 flagella, chromatophores, vacuole, stigma, etc., and are arranged 

 in four alternating rows with the sharp posterior ends pointing in 

 the same direction (Fig. 135, B). Reproduction is simultaneous in 

 all 16 cells and 16 daughter colonies result. Sexual processes are 

 unknown. 



The genus (Ionium is more specialized. The 16 cells of G. 

 pecioraJp and the 4 cells of (J. sociale are embeddetl in a gelatinous 

 matrix in such a manner as to form a flattened plate of cells with 

 the flagellated ends all turned in the same direction (Fig. 3, p. 21). 

 Here also each of the constituent cells forms an entire colony upon 

 reproduction. Fertilization by permanent union of isogametes is 

 characteristic; an encysted red-colored zygote is formed which 

 germinates after a period of quiescence. The 8-celled globular 

 colonies of StephanosphcBra have a similar life history (Fig. 135, A). 



Pandorina, Endorina and Platydorina are colonies of 16 or 32 

 cells, the first 2 globular, the last a flattened plate with charac- 

 teristic form (P'ig. 3, p. 21). In Pandorina, the 16, or rarely 32, 

 cells are pressed together in the center of the colony; in Endorina 

 they are distributed equally throughout the gelatinous matrix. 

 Anisogam^' appears to be facultative in Pandorina but obligatory 

 in Endorina where the colonies are sexually ditt'erentiated some 

 (male) giving rise only to microgametes in bundles of 64, others 

 (female) forming only macrogametes. Here also the encysted 

 zygotes are colored red. 



Phodorina and Volvox finally are colonies with permanently 

 difl'erentiated cells (Fig. 135, C and Fig. 136). The validity of the 

 genus Pleodorina is ciuestioned, Fritsch and Takeda (1916) for 

 example, regarding it as a variety of Eudorina which shows all 

 transition stages from a typical Eudorina to the conditions described 

 in the original Pleodorina illinoisensis, Kofoid (Crow, 1918). 



Order ^^ EUGLENroA, Stein. 



The Fuglenida comprising the fifth order of Phytomastigoda 

 include some of the largest and most common types of flagellates. 

 They are usually spindle form with a conspicuous periplast which 

 may be variously sculptured or striated, while keel-like processes 

 are occasionally present {Petalomonas, Tropidoscyphus). A gela- 

 tinous mantle in some cases is secreted (Colacium) and shells or tests 

 in others; these are soft and gelatinous in Ascor/lena, rigid and 

 frequently ornamented with papilhie, striations and spines in 

 Trachelovionas. jMetaboly is characteristic although the phenom- 

 enon is unknown for some genera and varies greatly in different 

 species. Spiral markings of the periplast are frequent and torsion 



