THE SERIAL RELATIONS OF INVERTEBRATA. 



579 



of the Gregarlnidm, Wimpyrella of the Heliozoa, Protomo- 

 nas of the ¥lagellata. A Moneran, ciliated over its whole 

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

 linina, Catallacta^ Tentacidlfera^ Clliata^ is at present un- 

 known. The Protozoa thus f4ll into the following series : 



I. 



Protozoa. 



II. III. IV. 



Protamoeba. Myxastrum. Vampyrella. 



Protogenes. 



Foraminifera. Protoplasta. Gregarinidoe. Heliozoa, 



Padiolaria. 



V. 



? 



Tentaculifera. 



VI. 



? 



Catallacta. 

 Opalinina. 

 Ciliata. 



VII. 



Protomonas. 



I 



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 

 MeUizoa^ though it is easy enough to imagine what such forms 

 might be. The spheroidal free-swimming mcmad aggregates, 

 such as JJvella and Polytorna^ and Magosphmra itself, are, 

 in many respects, comparable to Piiysemarian or Poriferan 

 embryos ; while an animal Vol^jox 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 TurheUarla. 



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- 

 doubtedl}', as E. van Beneden has suggested, represents a 

 type intermediate between the Protozoa and the Metazoa, 



