170 MORPHOLOGICAL DEVELOPMENT. 



But the relations of these lowest types to their environments 

 are comparatively so indeterminate, and onr knowledge of 



13? /JS 



* 3 * - J? 



their actions so scanty, that little beyond negative evidence 

 can be expected from the study of them. 



The like may be said of the Infusoria. These are more 

 or less irregular. In some cases where the line of move- 

 ment through the water is tolerably definite and constant 

 we have a form that is approximately radial — externally at 

 least. But usually, as shown in Figs. 137, 138, 139, there is 

 either an unsymmetrical or an asymmetrical shape. And when 

 one of these creatures is watched under the microscope, the 

 congruity of this shape with the incidence of forces is mani- 

 fest. For the movements are conspicuously varied and 

 indeterminate — movements which do not expose any two 

 or more sides of the mass to approximately equal sets of 

 actions. 



§ 245. Among aggregates of the second order, as among 

 aggregates of the first order, we find that of those possessing 

 any definite shapes the lowest are spherical or spheroidal. 

 Such are the Thalassicollce. These gelatinous bodies which 

 float passively in the sea, and present in turn all their sides 

 to the same influences, have their parts disposed with ap- 

 proximate regularity all around a centre. In some orders 

 of Foraminifera, as for instance the I^ummulites, we have 

 secondary aggregates the parts of which are spirally ar- 

 ranged, approximately in harmony with the radial relations 

 of the society to the environment ; but we have other types 

 in which the congregated units are distributed in ways not 

 easily definable, and having to the environment relations that 

 are obscure. Further, among these secondary aggregates in 

 which the units, only physically integrated, have not had their 



