THE SERIAL RELATIONS OF INVERTEBRATA. 



579 



of the Gregarinidai, Vampyrella of the Heliozoa, Protomo- 

 ?ias of the Flagellata. A Moneran, ciliated over its whole 

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

 linina, Gatallacta, Tentaculifera, Ciliata, is at present un- 

 known. The Protozoa thus fall into the following series : 



I. 



Protogenes. 



Protozoa. 



II. III. 



Protamoeba. Myxastrum. 



IV. 



Vampyrella. 



Foraminifera. Protoplasta. Gregarinidce. 



Heliozoa. 



i 



P^adiolaria. 



V. 



I 



Tent aculif era. 



VI. 



9 



VII. 



Protomonas. 



Gatallacta. 



i 



Opalinina. 



Giliata. 



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 Uvella and Polytoma, and Magosphc&ra 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 Pnfusoria, if it 

 became multinucleate, like an Opali?ia, would approach the 

 lowest Turbellaria. 



The axial cell of a JDicyema, 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 3fetazoa, 



