llECENt MEMOIRS ON FRESHWATER RHIZOPODA. 289 



of groups, in which a considerable number of characters in 

 common might have led to the supposition of a common 

 origin, they still have refrained from trying to subordinate 

 all the forms they met with to a single system. Efforts in 

 this direction have as yet produced but artificial schemes. 

 Thus, Claparede would separade Trinema and Euglypha 

 from Microgromia and Lecythium, and would place Arcella 

 and Difflugia far away, and in close proximity Avith Actino- 

 phrys and Heliozoa. Again, Avere there attributed to the 

 contractile vacuole a high systematic value, Lecythia would 

 stand more removed from Microgromia, Pleurophrys from 

 Trinema, than the latter from Actinophrys and other Helio- 

 zoa. So, things manifestly related would be dissociated, 

 forms standing remote would be combined. 



The authors in their systematic distribution go on the 

 following plan: they do not start from the consideration of 

 the group as a whole, and from certain prominent characters, 

 as do previous observers, but from the consideration of the 

 individual organisms ; and from an exact study of each form 

 they proceed to combine individual species into genera, and 

 these again into families and orders. But this plan they only 

 so far follow where a considerable sum of common characters 

 seemed to admit of their combination as one true to nature. 

 Forms which would not allow of being so subordinated they 

 prefer to allow to remain, ad interim, isolated, in order that 

 such exceptions should not disturb the certainty gained with 

 regard to certain groups of having only related forms in view. 

 By this inductive method the authors arrive at the assump- 

 tion that two " blood-related" groups become established, the 

 Monothalamia and the Heliozoa. Nearer relations between 

 them than would be expressed by the common subordination 

 of both to the Sarcodina the authors do not hold to exist. 



After the establishment of the foregoing two groups 

 founded on a blood-relationship, they have combined those 

 Sarcodina which remain over into a further group, in which, 

 however, no blood-relationship seems to be expressed amongst 

 the individuals thus brought together. 



I may be allowed here to remark that, referring to the 

 recent contributions of other observers besides Hertwig and 

 Lesser, there appears to me to be a general fault in the 

 formation of too many genera. I doubt not for a moment 

 the individuality and specific distinctness of the forms 

 brought forward, but it seems to me that each observer too 

 often makes a " new genus and species " for each form 

 whereas, for the present at least, it would seem more advis- 

 able, if the forms admit of it, to subordinate them to older 



VOL. XVI.— NEW SER. T 



