38 REVIEWS. 



Other writers go farther, and propose to unite the Sponges with the 

 Bhizopoda; nor can we hesitate to admit that many facts are in favour of 

 snch a conclusion. But, on the other hand, the possession of so remark- 

 able a morphological element as their fibre, which, even when siliceous, 

 as in Dictyochalis, still exhibits its characteristic reticulated arrang- 

 ment, must, apart from their aquiferous system, and the comparatively 

 large size which many of them attain, be duly estimated in all attempts 

 to lower the independent value of this group. 



The Gregarinida, at first sight, appear to depart most in structure 

 from the ordinary type of an Astomatous Protozoon. Yet even these, as 

 Lieberkiihn has shown, give rise, in the course of their development, to 

 bodies which very closely resemble Amaebae. Thus intimately are 

 these humbler organisms allied to one another. 



We are, therefore, disposed to conclude that the time has not yet 

 come for adopting any very definite sub-division of the Protozoa. Those, 

 however, who are not content with the simple enumeration of groups 

 given above, may adopt such a provisional arrangement as the follow- 

 ing :— 



PEOTOZOA. 



-A- > 



ASTOMATA. STOMATODA. 



>V. -A 



1. Bhizopoda. 1. Infusoria. 



2. Sponged a. 2. Noctiettcida. 



3. Gregarinida. 



Such characters as appear to be common to all the Protozoa are, for 

 the most part, purely negative. They do not present that differentia- 

 tion into distinct layers, which, at so early a stage of development, is 

 manifested by the members of the remaining sub-kingdoms. Those who 

 prematurely seek for a definition of the Protozoa must remember that, 

 in beings of the simplest plan of animal structure, the presence of j3osi- 

 tive anatomical features, similar to those which distinguish groups of a 

 higher grade of organization, is not to be expected. 



We look forward, then, with hope to the result of further investiga- 

 tions, for a solution of those difficulties which yet stand in the way of a 

 right knowledge of the Protozoa. Nevertheless, a writer so eminent as 

 Professor Agassiz has, in a recent work, declared that the very existence 

 of this division, as a distinct animal sub-kingdom, must henceforth be 

 ignored. We quote, verbatim, the passages in which he professes to 

 have arrived at so iconoclastic a conclusion: — 



" As to the Protozoa, I have little confidence in the views generally entertained re- 

 specting; their nature. Having satisfied myself that Colpoda and Paramecium are the 

 brood of Planarife, and Opalina that of Distoma, I see no reason why the other Infu- 

 soria, including in Ehrenberg's division Enterodela, should not also be the brood of the 

 manv lower worms, the development of which has hitherto escaped our attention. Again, 

 a comparison of the early stages of development of the Entomostraca with Rotifera might 



