PBOFESSOR W. G WILLIAMSON ON VOLVOX GLOBATOE. 329 



On examining a number of individuals, we shall find, 

 that whilst many of them contain young fac- similes of the 

 parent object, others exhibit no obvious traces of such young 

 organisms. The latter remark especially applies to those 

 small specimens which are the least developed. But even in 

 these a careful examination reveals a slight enlargement of 

 eight or nine cells, dispersed through different parts of the 

 structure (Fig. 1 d). This enlargement goes on until each 

 of the cells referred to, attains to a diameter four or five 

 times greater than those by which it is surrounded {Fig. 2 c). 

 The inner membrane also continues in close union with 

 the cell-wall, and never assumes the stellated contour seen 

 in the ordinary cells. In fact, the process begins whilst the 

 germs are contained within the parent; and before the 

 contents of any of the cells have become detached from the 

 cell-walls {Fig. 3 h). Two new cells are soo.i seen to have 

 been developed within the old one; and, by a repetition of a 

 similar process, each of these becomes the parent of two 

 more {Fig. 4 f). I have never yet observed one of these 

 germs within which eight cells could be seen at once. I have 

 no doubt that this arises from the fact, that the subsequent 

 division has taken place in the plane of the external surface, 

 and at right angles to the axis of vision. The next obvious 

 development always increases the number to sixteen {Fig. 8), 

 at which stage an internal cavity appears to have been 

 formed within the germ. From this point, the multiplica- 

 tion of cells, by the ordinary process of cell-development, 

 progresses {Figs. 9 and 10), until at length a condition is 

 attained, beyond which no farther increase takes place in 

 their number. It is at this stage, apparently, that each cell 

 is furnished with its pair of filaments. These appendages 

 are added before the young germ is set free by the rupture 

 of the parent, and occasionally the young ones may be seen 

 revolving within the old organism. This, however, is a 

 rare occurrence, since, though their ciliae move freely, the 



germs are usually stationary. 



2u 



