THE SKIMAI. KKI, \TI<>NS OF INVERTEBRATA. 579 



of the #/'.</'//>'///</", \'<tnti>!/r>Il of the Heliozoa, Protomo- 

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

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

 /////yj, Catallacta, Tentacidifera, Ciliata, is at present un- 

 known. The Protozoa thus fall into the following series : 



PROTOZOA. 



I. II. III. IV. 



Protogenes. Protamceba. Myxastrum. Vampyrella. 



Foraminifera. Protoplasta. Gregarinidce. Heliozoa. 



Eadiolaria. 



V. VI. VII. 



? ? Protomonas. 



Tentaculifera. Catattacta. Flagellata. 



Ciliata. 



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 in uiad aggregates, 

 such as Uvella and Polytorna, and Magosphwra itself. 

 in many respects, comparable to Pnysemarian or Poriferan 

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

 nent vesicular morula. So, one of the higher T/////X. //'.?, if it 

 became mnltinucleate, like an Opalina, would approach the 

 lowest Turbellaria. 



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

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

 tain extent, comparable to the capsule of a Ha.liolarian; 

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

 ate cortical layer would approach the structure of />//// 

 And if what is at present known of l>i< >j> ///'/ givey a just 

 conception of the essential points of itsentiiv historv, it un- 

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

 type intermediate between the Protozo / and the M> A 



