216 Dr. G. C. Wallich on the Extent and Causes of 



appeared in the ' Annals' during the course of the bygone year. 

 On the present occasion I propose to show that amongst the 

 testaceous genera of the same order (namely, the Proteina*) this 

 tendency to variation is no less marked, and that it is attribut- 

 able (as was stated to be the case in the non-testaceous genera) 

 rather to the ever-fluctuating conditions of the medium by which 

 the organisms are surrounded than to any special hereditary 

 idiosyncrasies by which certain characters become impressed upon 

 certain races of individuals. 



The primary points to be considered are, whether the degree 

 of variation observable in the soft parts — or actual bodies of these 

 creatures — is at all commensurate with that which is traceable in 

 their tests ; and whether there exists such an intimate relation 

 between the changes in figure, composition, size, and colour of 

 the tests, and of the savcode-bodies over which they are fc»rmed, 

 as to indicate varying degrees of physiological advance or de- 

 gradation. For it cannot be too strongly urged that, on the 

 proper apprehension of these two questions must mainly depend 

 our ability to discriminate between characters that are, and those 

 that are not, of true specific value ; and that every incautious 

 addition to our lists of species, whilst inevitably operating as 

 an obstacle in the path of those persons who are desirous of 

 studying the biological relations of the lower forms of organic 

 being, must also tend materially to augment the difficulties which 

 stand in the way of a natural and easily available systematic 

 arrangement. 



As stated by me in the 'Annals' for June last (p. 452), 

 it seems almost impossible to examine the sarcode-body of 

 Diffiugia and Arcella, on the one hand, and of Euglypha and 

 some allied forms, on the other, without perceiving that in 

 each case these organisms ought to be comprehended under a 

 single genus. Between the degree of differentiation attained by 

 the sarcode oi Difflugia and Arcella there is nothing suggestive 

 of more than specific distinctness. Both these forms are Amoeba 

 in the strictest sense ; that is to say, their bodies consist of sar- 

 code in which the degree of consolidation of the external layer 

 for the time being is so complete that the outline of the surface, 



* Under this designation are united by me those Rhizopods which differ 

 from the preceding orders (namely, the Herpnemata and Protoderraata) in 

 the possession both of a definite nucleus and contractile vesicle. They are 

 divisible into two primary famihes, the "Amcebina " and " Actinophryna," 

 based principally on peculiarities presented by the sarcode-body. 



The Difflugidce constitute a subfamily of the Amabina standing natu- 

 rally apart from the remaining testaceous forms which present the Actino- 

 phryan type of cctosarc and pseudopodia, and hence constitute a subfamily 

 of the Actinophryna under the name of the Euglyphid(S. (See classifica- 

 tion of these subfamilies, at page 240^. 



