338 PROFESSOE W. C. WILLIAMSON ON VOL VOX GLOBATOK; 



In the development of the young germs of Volvox, we 

 have a process closely resembling that by which the em- 

 bryos of all phaneroganic plants are formed ; for vrhilst it 

 is seen amongst the ova of animals, it is also one of the 

 ordinary phenomena of vegetable life^ 



The cells of Volvox, in their varying conditions, throw 

 some light upon an interesting problem in physiological 

 botany, since they may probably be regarded as the proto- 

 types of a structure found in some of the higher plants. 

 The cells entering into the composition of the hard endo- 

 carps of such fruits as the plum, and even the pear, are, as is 

 well known, lined by successive layers of sclerogen. These 

 layers are penetrated by tubular extensions of the central 

 cavity, the extremities of these tubes being usually in con- 

 tact with the corresponding ones of adjoining cells, as in 

 the case of the radiating prolongations of the inner cell- 

 membrane of Volvox. Now it appears probable, that we 

 have here the same phenomena under different conditions. 

 Dr. Carpenter inclines to the opinion, that as the inner 

 cell-membranes become detached from the outer cell-walls 

 in the plum-stone, they throw off successive layers of sclero- 

 gen, which occupy what would otherwise have been an 

 intervening cavity. In the Volvox we have the same reces- 

 sion of the inner from the outer cell- wall ; but we have not 

 the cognate development of sclerogen ; the intervening 

 space being merely filled with colourless fluid. The struc- 

 ture of the Volvox cell thus appears to give support to Dr. 

 Carpenter's explanation of those of hard endocarps, an ex- 

 planation which equally applies to the development of most 

 forms of pleurenchyma. 



We thus find, that a vegetable analogue is to be found for 

 every portion of the structure of Volvox, as well as of every 

 function which those structures fulfil, so far as we can com- 

 prehend them. But on comparing it with known and un- 

 doubted animal organisms, we find that it is wanting in 



