OF ANIMATE BEINGS. 13 



here is one instance among many others in which the muscular 

 action of a scarcely organized body is as rapid as in the most 

 highly perfected types of animals. 



The circulation of the fluid and granular contents of the body 

 is more active than in Amoeba, but it does not appear to be at 

 all different in kind or of a more complicated nature, although 

 it seemingly is so because it has the appearance of being con- 

 fined in more restricted channels, as it passes along the slender 

 pseudopodia ; but these channels are mere hollows with as in- 

 definite boundaries as in Amoeba. 



From this we may infer that it is not by a general advance 

 of the whole organization that the upward steps, in the develop- 

 ment of types, are made ; but here and there one organ after 

 another is either added, or more and more specialized in its 

 functions, until, by insensible grades, the highest type of organ- 

 ization within each group is attained. 



In this other figure, (fig. 3,) which represents an animal which 



I kept by hundreds in my marine aqua- 

 rium for eighteen months, the advance 

 in grade is made by a simple compli- 

 cation of the covering of the body ; 

 F5 s- 3 - merely by elongating and coiling the 



dormitory of the little creature, so as to resemble the spiral shell 

 of some of the snails. The pseudopodia (b) are exceedingly trans- 

 parent, pointed, and so excessively slender toward their tips that 

 it requires the best powers of the microscope to see them ; but 

 yet, upon the least disturbance, these frail threads retract their 

 length down to almost nothing, with a lightning-like rapidity ; 

 even while you are looking at them there is a sudden shock, 

 and they are gone ! 



How slight indeed is the degree of organization required in 

 which to manifest some of the most active powers of vitality ! 

 Almost within a step we have the dazzling complication of the 



Fig. 3. Cornuspira planorbis. Schultze. 50 diam. Represented as it crept 

 over the glass side of the aquarium, a, the shell ; 6, the pseudopodia, par- 

 tially extended backward over the surface of the shell. Original. 



