PROTOCOCCUS PLUVIALIS. 549 



cell around them, thus becoming encysted zoospores, 

 differing from the larger form of that kind only in size 

 (Fig. 41). 



The author once observed four cells arranged as it 

 were in a cross, and connected to each other by the 

 anterior end (Fig. 25), and which, from their struc- 

 ture, appeared to be referable to the encysted motile 

 zoospore. It is a very remarkable circumstance, and one 

 difficult of explanation, that in this case each of the four 

 larger primordial cells was connected with each of the 

 two contiguous cells by two transverse processes, which 

 passed through the enveloping cell-membrane. In this 

 respect there was a resemblance to Chlamidomonas pul- 

 visculus and Trachelomonas volvocina, Morren, which re- 

 main connected by the beak or vibratile cilia. (' Recherch. 

 sur la Rubefact.,' Tab. II, fig. iii b, Tab. V, figs. 9, 8.) 

 I think, however, that this condition is to be explained 

 upon the supposition that four primordial cells have been 

 formed within a parent cell by the usual mode of seg- 

 mentation, but that instead of their being completely sepa- 

 rated from each other, they remain connected, and that 

 then, after resorption of their common, parent enveloping- 

 cell, also develope in the usual way special enveloping-cells, 

 which are of course in contact in the centre, and necessa- 

 rily assume a cruciate figure. A smaller portion, which 

 in the organisation of the segments was not taken into 

 any of them, has become an independent but more 

 minute primordial cell, lying between the arms of two of 

 the primordial cells constituting the cross. The above 

 process seems to be analogous to what takes place in 

 Gonium, or Volvox, in which the individual segments, 

 after division, are retained in connexion. 



Having thus gone over the various morphological and 

 developmental conditions of the Protococcus, the author 

 proceeds to its biology. 



The most striking of the vital phenomena presented 

 by this organism is that of periodicity. Certain forms, 

 for instance encysted zoospores, or certain colours, ap- 



