1886.] 



MICKOSCOPICAL JOURNAL. 



235 



for separate prints of which ^ve are 

 indebted to the author, that are 

 worthy of careful attention. 



■ The first is entitled, ' Critical Notes 

 on Dr. A. Gruber's Contribvitions to 

 the Knowledge of the Amoebae,' 

 which has already been noticed in 

 these columns. It will be remem- 

 bered that Dr. Gruber put forward 

 certain views relative to the nuclei 

 and their importance in the discrimi- 

 nation of species, and discussed the 

 general structure of these organisms. 

 Dr. Wallich reviews the article of 

 Dr. Gruber at some length, and crit- 

 icises his conclusions. As regards 

 nuclei, Dr. Wallich considers that 

 their number may vary to ' any mod- 

 erate extent,' and cites the case of 

 Arcella vulgaris^ which sometimes 

 shows several nuclei ; in one speci- 

 men six were distinctly seen. This 

 specimen had also nine peripheral 

 contractile vesicles. In the main, 

 however, Dr. Gruber's observations 

 in regard to the relations of endosarc 

 and ectosarc and the phenomena of 

 movement have led him to conclu- 

 sions quite in accord with those held 

 by Dr. Wallich, and by him pub- 

 lished long ago. 



The second contribution is entitled, 

 'Critical Observations on Prof. 

 Leidy's " Fresh-Water Rhizopods of 

 North America," and Classification 

 of the Rhizopods in General.' This 

 is an interesting review of some of 

 the literature pertaining to the sub- 

 ject, but it is too lengthy for satisfac- 

 tory notice here. We can only al- 

 lude to a few of the criticisms which 

 the author makes of Prof. Leidy's 

 excellent work. 



Dr. Wallich first maintains that he 

 had fully established the presence of 

 both a nucleus and a contractile vesi- 

 cle in Gromia^ and that he no longer 

 regarded it as a typical reticularian 

 form, but as early as 1865 had shown 

 that it belonged to the highest type 

 of rhizopod structure. 



Through a very curious and un- 

 fortunate misapprehension, Dr. Leidy 

 seems to have mistaken Dr. Wallich's 



account of the varieties of Dijfflugia 

 proteifoi-niis and D. p v r ifo r m is 

 which were described in 1864. Dr. 

 Leidy refers these forms to Nebela^ 

 and alludes to them as ' described as 

 transition forms of D. symmetrica^ 

 although Dr. Wallich did not so de- 

 scribe them. Evidently there has 

 been an error, and a very curious 

 one. 



Dr. Wallich does not approve of 

 the generic distinction ^tiadrula, 

 the only species of which is ^. sym- 

 metrica^ Leidy. He maintains that 

 the species so named is identical with 

 his Diffliigia symmetrica. More- 

 over, Dr. Wallich doubts the value 

 of the many specific distinctions 

 which Prof. Leidy makes under the 

 genus Di-ffiugia^ and considers that 

 the seven types of the genus described 

 by himself include also all of Prof. 

 Leidy's Nebelce. 



The discussion of the relations of 

 the rhizopod tests, and their signifi- 

 cance in classification, cannot be sat- 

 isfactorily treated in this place. Dr. 

 Wallich has presented the subject in 

 a masterly manner, and we must re- 

 fer the reader to his article. We es- 

 pecially commend this subject to the 

 consideration of observers. Certainly 

 the innumerable variety in form and 

 texture of the tests cannot afford a 

 sufficient character for distinguishing 

 species, even in such a blind and arti- 

 ficial system of classification as we 

 now have for the rhizopods. Con- 

 sider the Foraminifera for a moment. 

 What great variations in the shells we 

 find among them, yet how closely they 

 are related in plan of growth. Exter- 

 nal form can only be regarded as a 

 specific feature when we discover it 

 to be reasonably constant under dif- 

 ferent conditions ; and even then it is 

 only a convenient character for pur- 

 poses of description and recognition 

 of forms. H. 



Prof. Hitchcock has informed us 

 that he desires to change the conjec- 

 ture of his in the letter ' Jottings by 

 the Way,' September number of this 



