THE MORPHOLOGICAL COMPOSITION OF ANIMALS. 87 



Fig. 134, has a denser coating formed of agglutinated foreign 

 particles; so that the protrusion of the pseudopodia is limited 

 to one part of it. And in the solitary Foraminifera, like 

 Gromia, the sarcode is covered over most of its surface by a 

 delicate calcareous shell, pierced with minute holes, through 

 which the slender pseudopodia are thrust. The 



Gregarina exhibits an advance in integration, and a conse- 

 quent greater definiteness. Figs. 135 and 136, exemplifying 

 this type, show the complete membrane in which the sub- 

 stance of the creature is contained. Here there has arisen 

 what may be properly called a cell: under its solitary ? orm 

 this animal is truly unicellular. Its embryology has con- 

 siderable significance. After passing through a certain qui- 

 escent, " encysted " state, its interior breaks up into sn. all 

 portions, which, after their exit, assume forms like that of 

 the Amoeba; and from this young condition in which they 

 are undifferentiated, they pass into that adult condition in 

 which they have limiting membranes. If this development 

 of the individual Gregarina typifies the mode of evolution of 

 the species, it yields further support to the belief, that frag- 

 ments of sarcode existed earlier than any of the structures 

 which are called cells. Among aggregates of the first 



order, there are some much more highly developed. These 

 are the Infusoria, constituting the most numerous of the 

 Protozoa, in species as in individuals. Figs. 137, 138, and 

 139, are examples. In them we find, along with greater 

 definiteness, a considerable heterogeneity. The sarcode of 

 which the body consists, has an indurated outer layer, bearing 

 cilia and sometimes spines; there is an opening serving as 

 mouth, a permanent oesophagus, and a cavity or cavities, 

 temporarily formed in the interior of the sarcode, to serve as 

 one or more stomachs; and there is a comparatively specific 

 arrangement of these and various minor parts. 



Thus in the animal kingdom, as in the vegetal kingdom, 

 there exists a class of minute forms having this peculiarity, 

 that no one of them is separable into a number of visible 



