46 
Williamson 07i Volvox glohator. 
No one who has seen these specimens can for a moment 
doubt that there exists immediately beneath the superficial 
pellicle, or common investing membrane of each Volvox, a 
layer of closely-packed translucent vesicles, within each of 
which is located one of the numerous green spots ornamenting 
its periphery. In the memoir referred to, T endeavoured to 
show that these vesicles are true cellsj whilst the green spots 
are the inner cell-membranes and their contents, representing 
the internal utricles of Harting and Mulder, the primordial 
utricles of Mirbel. The appearance of these cells in their 
different stages of growth was described, and the mode of 
their development and multiplication examined. 
Mr. Busk, who has recently directed his attention to this 
subject, has arrived at a different conclusion from my own, 
respecting the structures in question. Not having, then, seen 
the hyaline vesicles, which I regard as true cells, in any of his 
own specimens, he concluded that the Volvox consists of a 
number of protoplasms, which have resulted from the suc- 
cessive segmentations or subdivisions of one primary pro- 
toplasm, in the way described in my memoir. On being 
afforded an opportunity of examining some of my preparations 
of Volvox made last year, and in which the vesicles are re- 
markably distinct, though the appearance they presented was 
wholly new to him, he was still disposed to maintain his pre- 
vious opinion. Instead of admitting them to be true cells, 
he concluded that they were merely the outer layers of the 
protoplasmic segments, which, after separating from the pro- 
toplasmic mass, had become dropsically distended, and as- 
sumed the appearance of a true cell. 
Since I believe this general conclusion to be incorrect, I am 
anxious to render more clear than I have hitherto done, what 
appears to be the true interpretation of the structures in ques- 
tion. In accomplishing this, it will not be necessary to reca- 
pitulate all the details of my preceding memoir, since the 
accuracy of the greater number of them, as well as my con- 
clusion respecting the vegetable nature of Volvox, are con- 
firmed both by Mr. Busk and by other observers : some 
points, however, require to be examined in detail. 
There is one point respecting which I was clearly in error ; 
my present correction of the mistake is due to the suggestions 
which I have received from Mr. Busk. I found that each 
young germ was developed from one of the peripheral stratum 
of cells, by the ordinary process of cell-division or segmenta- 
tion. Having ascertained that each protoplasm in its matured 
state was invested by a true external cell, in addition to a very 
thin inner one which held the granular mass together, I con- 
