94 MORPHOLOGICAL DEVELOPMENT. 



viduals, though severally originated by gemmation from the 

 same germ, have but little physiological dependence. In 

 kindred kinds, however, as shown in Figs. 154 and 155, one 

 of which is a magnified portion of the other, the integration 

 is somewhat greater: the co-operation of the united indi- 

 viduals being shown in the production of those tubular 

 branches which form their common support, and establish 

 among them a more decided community of nutrition. 



Among the Ascidians this general law of morphological 

 composition is once more displayed. Each of these creatures 

 subsists on the nutritive particles contained in the water 

 which it draws in through one orifice and sends out through 

 another; and it may thus subsist either alone, or in con- 

 nexion with others that are in some cases loosely aggregated 

 and in other cases closely aggregated. Fig. 156, Phallusia 



mentula, is one of the solitary forms. A type in which the 

 individuals are united by a stolon that gives origin to them 

 by successive buds, is shown in Perophora, Fig. 157. Among 

 the Botryllidce, of which one kind is drawn on a small scale 

 in Fig. 159, and a portion of the same on a larger scale in 

 Fig. 158, there is a combination of the individuals into an- 

 nular clusters, which are themselves imbedded in a common 

 gelatinous matrix. And in this group there are integrations 

 even a stage higher, in which several such clusters of clusters 

 grow from a single base. Here the compounding and re- 

 compounding appears to be carried further than anywhere 

 else in the animal kingdom. 



Thus far, however, among these aggregates of the third 

 order, we see what we before saw among the simpler aggre- 

 gates of the second order we see that the component indi- 

 vidualities are but to a very small extent subordinated to 



