40 REVIEWS. 



lay eggs, out of which Paramecia were born, which underwent all the changes these 

 animals are known to undergo up to the time of their contraction into a chrysalis state; 

 while the Opalina is hatched from Distoma's eggs. I shall publish the details of these 

 observations on another occasion. But if it can be shown that two such types as Para- 

 mecium and Opalina are the progeny of worms, it seems to me to follow that all the 

 Enterodela, with the exception of the Vorticellidse, must be considered as the embryonic 

 condition of that host of worms, both parasitic and free, the metamorphosis of which is 

 still unstudied. In this connexion I might further remark, that the time is not long 

 past when Cercaria was also considered as belonging to the class of Infusoria, though at 

 present no one doubts that it belongs to the cycle of Distoma; and the only link in the 

 metamorphosis of that genus which was not known is now supplied, since, as I have 

 stated above, the embryo which is hatched from the egg laid by the perfect Distoma is 

 found to be an Opalina." 



" All this leads to the conclusion that a division of the animal kingdom to be called 

 Protozoa, differing from all other animals in producing no eggs, does not exist in nature ; 

 and that the beings which have been referred to it have now to be divided, and scat- 

 tered, partly among plants, in the class of Algae, and partly among animals, in the classes 

 of Acephala, (Vorticelhe,) of Worms, (Paramecium and Opalina,) and of Crustacea, (Roti- 

 fera) ; the Vorticellas being genuine Bryozoa, and therefore Acephalous Mollusks ; while 

 the beautiful investigations of Dana and Leydig have proved the Rolifera to be genuine 

 Crustacea, and not worms." 



In these passages it will be observed that much which cannot be 

 accepted is blended with statements of facts long since admitted to be 

 true, and thus a certain degree of plausibility conferred upon the whole. 



Few, indeed, will deny that the Desmidia, Volvocinse, and several 

 other organisms referred by Ehrenberg to his Polygastrica, are true Algce. 

 That many of the Enterodela may yet prove to be embryonic forms 

 seems also highly probable. To conclude, however, that all the Infu- 

 soria, with the exception of the Yorticeliidse, may thus readily be dis- 

 posed of, appears at best a somewhat hasty mode of removing difficulties, 

 the solution of which must depend on a long series of patiently con- 

 ducted embryological inquiries. Because two or three forms of supposed 

 Infusoria are shown to be stages of development in the life-history of 

 certain worms, it by no means follows that all remaining Infusoria are 

 to be likewise so regarded. Nor does the careful examination of such a 

 genus as Pedicellina, which of all the Bryozoa most closely approaches 

 Vorticella in form, strengthen the opinion entertained by Prof. Agassiz 

 of their mutual relationship, but is rather decidedly opposed to it. 



The assertion that Rhizopoda have not yet found " a place generally 

 acknowledged as expressing their true affinities," would scarcely lead 

 the reader to suppose that Brown, Cams, Gegenbaur, Siebold, Yogt, Yan 

 Beneclen, Gervais, and many other zoologists, agree in referring them 

 to the type of Protozoa. And he who reads with care the memoirs of 

 Carpenter and Williamson on the shelly structure of the Foraminifera, 

 will scarcely be disposed to call in question their animal nature, or 

 liken the highly complex frame- work of Peneroplis or Polystomella to 

 the stony frond of a Melobesia, in every essential respect so different. 

 Still less does the sarcode substance of the Rhizopods and Sponges 

 resemble, in its vital endowments, the viscid contents of the vesicles 

 of Fuci. Lastly, it is incorrect to state that the Protozoa, as a group, 

 are distinguished from other animals in producing no eggs, since, even 



