OF PROTOZOA. 43 



self; so that in this respect sponges have as low a type of tissues 

 as the Rhizopods. 



But yet you must have seen, that, as I said at the beginning 

 of this description, the sponges have a degree of specialization, 

 of parts of the organization, that at once stamps them as of a 

 higher order of beings than the Amosbas and their congeners. 

 In addition to what may be found in the Rhizopods, we have in 

 the Sponges distinct channels of circulation, vibratile cilia giving 

 a direction to these currents, particular inlets and as definite an 

 outlet for the passage of food ; and in some of the peculiar forms, 

 the spiculae are arranged according to definite patterns about 

 the inlets and the outlet, thus adding an element of gradation, 

 while subserving the needs of an already distinctly specialized 

 function. 



The group of beings to which the next animal, that I shall in- 

 troduce to your notice, belongs, is one that in a certain sense is 

 more directly allied to Rhizopods than to Sponges, on account 

 of the mode of life which is prevalent among the members. But 

 what distinguishes the Actinophryians, as this group is called, 

 from the two foregoing is that they, at least some of them, have 

 a distinct cellular structure ; and yet, though the cells are very 

 distinct, they exhibit a low state of development, as low perhaps 

 as could possibly obtain without failing to be genuine cells. In 

 other respects the nature of the organization is very much like 

 that of Rhizopods. Still, from another point of view, the Actino- 

 phryians might be called a peculiar group of Sponges ; in fact, 

 there are some forms among them that are as yet in an un- 

 decided position, in the opinions of naturalists, as to whether 

 they are members of the latter or the former group. The truth 

 of the matter is, they form a transition from the one to the other, 

 of such insensible gradations that it is impossible to determine 

 where the one group ends and the other begins. It is on this 

 account, therefore, that out of these innumerable gradations I can 

 only present for your consideration those forms, in the progress- 

 ing scale of development, which exhibit such features as mark a 

 distinct step in the elevation of animal organization. 



