16 MORPHOLOGICAL DEVELOPMENT. 



finiteness, as well as increasing extent. In the yeast-plant, 

 Fig. 7, we have cells which may exist singly, or joined into 

 groups of several ; and which have their shapes scarcely at 

 all modified by their connexion. Among the Desmidiacece, it 

 happens in many cases, that the two individuals produced by 

 division of a parent-individual, part as soon as they are fully 

 formed ; but in other cases, instead of parting they compose 

 a group of two. Allied kinds show us how, by subsequent 

 fissions of the adherent individuals and their progeny, there 

 result longer groups ; and in some species, a continuous thread 

 of them is thus produced. Figs. 8, 9, 10, 11, exhibit these 



aeveral stages. Instead of linear aggregation, some of the 

 DesmidiaceoB illustrate central aggregation ; as shown in 

 Figs. 12, 13, 14, 15. Other instances of central aggrega- 

 tion are furnished by such protophy tes as the Gonium pector- 

 ale, Fig. 16 (a being the front view, and b the edge view), 

 and the Sarcina vcntriculi, Fig. 17. Further, we have that 

 spherical mode of aggregation of which the Voltox globator 

 furnishes a familiar instance. 



Thus far, however, the individuality of the secondary ag- 

 gregate is feebly pronounced : not simply in the sense that 

 it is small ; but also in the sense that the individualities of the 

 primary aggregates are very little subordinated. But on 

 seeking further, we find transitions towards forms in which 

 the compound individuality is more dominant, while the sim- 

 ple individualities are more obscured. Obscuration 

 of one kind, accompanies mere increase of size in the second- 

 ary aggregate : in proportion to the greater number of the 



