Ixxxii THE BEGINNINGS OE LIFE. 



transparent glass vessels, others in semi-transparent and 

 green ones, others in porcelain, and others again in perfectly 

 opaque cups, the modifications in size and figure according 

 to the intensity of Hght they received were altogether in- 

 credible. In the opaque vessels where they got little light, 

 the green cells remained delicate, small, and widely dispersed, 

 whilst in the transparent glasses, under sunlight, they became 

 many times larger and crowded together, and their figure 

 fusiform, irregular, and produced into numerous protoplasmic 

 processes. Indeed, on placing two portions of the same col- 

 lection of Stephcmosph(xra-g\obQS, the one in a transparent, 

 the other in an opaque vessel, the swarming individuals in 

 the two will be found so unlike that they might be readily 

 conceived to be different species.' 



With regard to the range of variation possible in any 

 one species, the researches of Cohn ^ on the development of 

 P?-otococcus pluvialis have revealed the most startling facts. 

 Summing up the developmental stages, which he had pre- 

 viously given in detail, he says (p. 559) : — ' Thus we see that 

 a single species, owing to its numerous modes of propagation, 

 can pass through a number of very various forms of develop- 

 ment, which have been either erroneously arranged as dis- 

 tinct genera, or at least as remaining stationary in those 

 genera, although, in fact, only transitionary stages. Thus 

 the still Protococcus cell (Fig. 2) corresponds to the common 

 Protococcus coccoma (Kiitz.). When the border becomes 

 gelatinous it resembles P. pulcher (Fig. 70) ; and the small 

 cells P. minor. The encysted motile Zoospore is the genus 

 Gyges granulum among the Infusoria, resembling also on 

 the other side P. turgidus (Kiitz.), and perhaps P. versatilis 

 (Braun). The Zoospores divided into two (Figs. 23, 30) 

 must be regarded as a form of Gyges bipartitus, or of P. di- 



^ See Translation of his Memoir, with plates, in ' Botan. and Physiolog. 

 Memoirs,' Ray Soc, 1853. 



