288 ESSAY ON CLASSIFICATION. 



The fundamental groups adopted by Vogt 1 are : Pro- 

 tozoa, Kadiata, Vermes, Mollusca, Cephalopoda, Articulata, 

 and Vertebrata, an arrangement which is based solely 

 upon the relations of the embryo to the yolk, or the ab- 

 sence of eggs. But, as I have already stated, this is an 

 entirely unphysiological principle, inasmuch as it assumes 

 a contrast between the yolk and the embryo within limits 

 which do not exist in nature. The Mammalia, for in- 

 stance, which are placed, like all other Vertebrata, in the 

 category of the animals in which there is an opposition 

 between the embryo and the yolk, are as much formed of 

 the whole yolk as the Echinoderms or Mollusks. The yolk 

 undergoes a complete segmentation in the Mammalia, as 

 well as in the Kadiates, the Worms and most Mollusks ; and 

 the embryo, when it makes its appearance, no more stands 

 out from the yolk than the little Starfish stands out from 

 its yolk. These simple facts, known since Sars and 

 Bischoff published their first observations twenty years 

 ago, is in itself sufficient to show that the whole principle 

 of classification of Vogt is radically wrong. 

 Eespecting the assertion, that neither Infusoria nor 



Minting radiating partitions, project- kind as those that project around the 

 ing inward from the outer wall of upper margin of the main cavity, 

 the body into the main cavity, and Again, the marginal tentacles of the 

 in having a digestive cavity derived Acalephs are homologous to those of 

 from the inversion of the upper part the Polyps, while their oral append- 

 of that wall into the upper part of ages are characteristic of their class. 

 the main cavity. In Acalephs there I may add also that the radiating 

 are no radiating partitions, and the partitions of the Rugosa, which I re- 

 digestive cavity is hollowed out of fer to the Acalephs, as well as the 

 the mass of the body ; the central Tabulata, are not homologous to the 

 prolongation of the body rising above radiating partitions of the Actiuoids 

 the digestive cavity in the shape of and Halcyonoids, but correspond to 

 oral appendages, which are never the ridges of the stem of certain Hal- 

 hollow as the tentacles of the Polyps cyouoids, and are, like them, a foot 

 are. The mouth tentacles of Cerian- secretion. v 

 thus, which are hollow, are not ho- l VOGT (CARL), ZoologischeBriefe. 

 mologous to the oral appendages of Naturgeschichte der lebenden und 

 the Acalephs, but constitute only an untergegangenen Thiere. Frankfurt 

 inner row of tentacles, of the same a M., 1851 ; vol. i, p. 70. 



