628 SCIENCE PROGRESS 



only a thin layer of protoplasm separates this eye-spot from 

 the cell-wall, which forms the external boundary of the 

 C/damydomonas-md\v\dua\ and is provided with two delicate 

 pores at the front end for the protrusion of the cilia. Under 

 normal conditions the Chla?)iydomonas-'mdiv\dua\ moves actively 

 through the water with the ciliated end directed foremost, 

 while the body at the same time rotates on its own axis. It 

 shows marked chemotactic and phototactic sensitiveness, being, 

 for instance, attracted by light not exceeding a certain degree 

 of intensity. 



Asexual (or vegetative) reproduction is effected simply by 

 subdivision of the individual (fig. i, b-d). The cilia are drawn 

 in or cast off, the nucleus divides, the pyrenoid becomes doubled, 

 and thereupon the cell-contents undergo gradual constriction 

 into two halves. One or two further divisions generally take 

 place in planes at right angles to the first. The daughter- 

 individuals, while still lying within the mother-cell, become 

 enveloped by new walls of their own, cilia appear, and ultimately 

 the products of division (comparable to the zoospores of the 

 higher types) are liberated as motile elements identical, except 

 as regards their smaller size, with the mother-individual. The 

 direction of the first division-wall is not the same in all the 

 species of Chlamydomonas, and constitutes a point of some im- 

 portance (Dill 21). In certain species of the genus (e.g. 

 C. angulosa, C. gigautea, also in the allied genera Chloromonas 

 and Carteria), the first division is longitudinal (fig. i, b), being 

 effected by a constriction appearing both at the front and 

 back end of the cell ; in these cases the second division is 

 generally also longitudinal. In the majority of species (e.g. 

 C. Reinhardi), however, the first division-wall is at right angles 

 to the longitudinal axis of the cell. These two cases are con- 

 nected by intermediate forms ; thus in C. longistigma the first 

 division commences in a direction parallel to the longitudinal 

 axis, but before the process of constriction is complete rotation 

 to the transverse plane (fig. i, c, d) takes place (in from thirty 

 to forty minutes), so that the division comes to resemble that 

 of the second type. Oltmanns (53, p. 143) has suggested that 

 the first division may in all cases be a longitudinal one, but 

 that in many species rotation to the transverse plane takes 

 place at such an early stage that it is not recognisable ; this 

 view is based on the consideration that symmetrical halving of 



