Miscellaneous. 275 



At the time of fecundation the bundles of antherozoids are set at 

 liberty by the dissolution of the wall of the antheridium ; they move 

 rapidly in the water, and hasten to fix themselves on the female 

 ccenobia. There they break up to allow the antherozoids to fecun- 

 date the oospheres ; but I have been unable hitherto to observe the 

 moment of their penetration. 



After fecundation the oospheres surround themselves with a thick 

 membrane with a double contour, which until then was invisible, 

 and rapidly change colour : from a dark green they become yellowish 

 green, then orange. They then contain a red oily matter and a 

 large quantity of starch. It is this orange colouring which led some 

 observers to believe that there was a third species of Volvox ( Volvox 

 aureus, Ehr.). 



The Volvoces, male, female, and neuter, seek light, either solar or 

 artificial, and keep near the surface of the water. As soon as the 

 female ccenobia are fecundated and the oospores change colour, they 

 are seen to avoid the light and to depart from the surface of the 

 water. It is easy to observe this phenomenon in a glass pan or iu 

 a watch-glass ; the green Volvoces stay on the light side, the others 

 on the diametrically opposite. If the glass is turned they change 

 places respectively ; and this transfer is effected in a very short time. 

 The Volvoces with orange oospores move much more rapidly from the 

 light than the others towards it. The displacement of the Volvoces 

 is owing, as is well known, to the movement of the two vibratile 

 cUia with which each vegetative cell is provided, and which project 

 beyond the gelatinous sphere. No change of colour or form can be 

 observed in these cells after fecundation ; we are therefore led to 

 think that it is by a sort of attraction exerted on the green matter 

 that the Volvoces are drawn towards the light, and that it is by a 

 sort of repulsion exerted on the red matter of the fecundated gyno- 

 gonidia that these same Volvoces afterwards seek obscurity. 



When the Volvoces begin to appear in the waters where they are 

 found, scarcely any but neuter ccenobia are met with — that is to 

 say, ccenobia enclosing only vegetative cells giving birth by segmen- 

 tation to daughter-colonies. When some time has passed the 

 number of daughter-colonies contained in each coenobium diminishes ; 

 but there then appear in many Volvoces some androgonidia, Avhich 

 represent abortive daughter-colonies. At this moment we only find 

 a few female Volvoces not containing any daughter-colonies. When 

 the Volvoces have thus reprodufeed themselves for a certain time by 

 daughter-colonies, the number of female ccenobia is increased, and, 

 some exclusively male ccenobia, destitute of daughter-colonies, appear, 

 while the neuter ccenobia become very rare. 



It results from these facts that during a certain period the Volvox 

 is multiplied by asexual generation, by scissiparity of a vegetative 

 cell, which by successive segmentations produces a colony of indi- 

 viduals similar to the mother-colony to which this cell "belonged. 

 But a time comes when the vegetative cell no longer possesses the 

 property of reproducing itself thus ; it can still divide into segments, 

 and give birth to a colony of little cells which acquire a sexual 

 character ; that is to say, they are incapable of living separately 



