THE SERIAL RELATIONS OF INVERTEBRATA. 



579 



of the Qregarinidaz, Vampyrdla of the ITeliozoa, Protomo- 

 nas of the Plagellata. A Moneran, ciliated over its whole 

 surface, which might stand in the same relation to the Opa- 

 linina, Catallacta, Tentacidifera, Ciliata, is at present un- 

 known. The Protozoa thus fall into the following series : 



Protozoa. 



Proto genes. 

 Foraminifera. 



II. 



Protamoeba. 



Protoplasta. 



III. 



Myxastrum. 



Gregarinidce. 



IV. 

 Yampyrella. 



Heliozoa. 



i 



Padiolaria. 



V. 



9 



Tentaculifera, 



VI. 



? 



Catcdlacta. 

 Opalinina. 



Ciliata. . 



VII. 

 Protomonas. 



Flagellata. 



I am unable to trace any one of these series of modifica- 

 tions further ; that is to say, to find forms which actually 

 bridge over the interval between any one of them and the 

 Metazoa, though it is easy enough to imagine what such forms 

 might be. The spheroidal free-swimming monad aggregates, 

 such as Tlvella and Polytoma, and Magosphmra itself, are, 

 in many respects, comparable to Physemarian or Poriferan 

 embryos ; while an animal Vblvox would be a sort of perma- 

 nent vesicular morula. So, one of the higher Infusoria, if it 

 became multinucleate, like an Opalina, would approach the 

 lowest Turbellaria. 



The axial cell of a Dicyema, from the protoplasm of which 

 its ciliated and nonciliated germs are produced, is, to a cer- 

 tain extent, comparable to the capsule of a Radiolarian ; 

 while, on the other hand, a Radiolarian with a multinucle- 

 ate cortical layer would approach the structure of Dicyema. 

 And if what is at present known of Dicyema gives a just 

 conception of the essential points of its entire history, it un- 

 doubtedly, as E. van Beneden has suggested, represents a 

 type intermediate between the Protozoa and the 3Ietazoa, 



