283 HICKSj ON MOTIONLESS SPORES OF VOLVOX GLOCATOR. 



It is well known that towards tlie end of autumn the 

 zoospores, instead of tending in the usual manner towards the 

 formation of the gemmules after the parent type, become 

 irregularly developed in that direction, and also into a condi- 

 tion which might, perhaps, be called an arrest in development, 

 being in this state set free by the destruction of the old 

 Vol vox. 



Let us take up our examination at the point where, in the 

 usual order of gemmule growth, the division of the zoospore 

 has continued to the formation of about thirty-six cells within 

 the common cell- wall (PI. IX, fig. 1). These, in the ordi- 

 nary way, would pass on to further subdivision, producing 

 almost from this point ciliated cells, which, again redi^iding, 

 would produce the ultimate zoospores held together by the 

 hollow, spherical membrane, or, in other terms, the ordinary 

 Volvox. Instead, then, of the subdivision forming the ciliated 

 cells, which tend towards the exterior of the mass, motionless 

 spores or gonidia are produced, which do not tend outwardly, 

 but which retain their position, except that they become more 

 separated from each other by the increase of the intervening 

 mucus. Watching these throughout the period above men- 

 tioned, I found that the segmentation continued in various 

 modes till the masses became one eighth of an inch in dia- 

 meter, preserving more or less of a globular form, but inde- 

 finite so far as any investing membrane was concerned. 



At first the division went upon the binary plan (fig. 2), 

 after which some of them divided into three or four segments, 

 — the division being cruciate — while others extended them- 

 selves in a linear series, Avith their short diameters in a line 

 (fig. 3). These are shown magnified, with nuclei, at fig. 3'. 

 Some of the divisions, instead of subdi\dding, increased in 

 size, producing a green cell much larger than the rest (fig. 3'). 

 At fig. 4 are two pairs of cells enclosed in a common mucous 

 envelope, much larger than the ordinary size. I have shown 

 at fig. 4 — 11 difi'erent varieties of the segmentation of 

 these motionless gonidia, forming in the last (fig. 11) a mass 

 not dissimilar to that of Tetraspora. 



The mucus which formed around these cells was at first 

 more or less definite in boundary, but after segmentation had 

 advanced to some degree its outline was irregular, and at last 

 quite indefinite. The outer edge never possessed more 

 solidity than the mucous envelope of Cladonia gleoccipsa. 



It is worthy of note that this condition I have seen to 

 commence ivithin the parent Volvox, before separation. 



Some of these forms will be recognised as analogous to 

 those which occur during the growth of Pandorina and in 



