Dr. Wallich on the RMzopods. 453 



authorize me in regarding the Ceratium of the Lake of Geneva 

 as the Ceratium Mrundinella, O. F. Mliller, described by 

 Bergh, and further in seeing in Cer-atiitni reticulatum, Imhof, 

 only a simple member of the cycle of variability to which this 

 old species, like so many others, is subject. 



EXPLANATION OF PLATE XII. Figs. 4-9, 



(All the figures enlarged 300 diameters.) 



Fiff, 4. Cuirass of a Cei'atium Mrundinella, seen from its dorsal surface. 



a, anterior horn ; b, posterior horns ; c, cincture ; d, ventral 



aperture. 

 Fig. 5. Ceratium hirundineUa, seen from its dorsal surface. Only the 



outlines of the cuirass are drawn, ex, exoplasm ; en, endoplasm ; 



gk r., red globules ; gl, g., fatty globules ; n, nucleus j nu, 



nucleolus. 

 Fig. 5 his. Nucleus of a Ceratium Mrundinella treated with picro-sulphuric 



acid and stained with acetic carmine. 

 Fig. 6. Ceratium Mrundimlla, drawn in the living state and then fixed, 



seen from the ventral surface, f, flagellum. 

 Fig. 7. Ceratium hirundineUa, seen from the dorsal surface. 

 Fig. 8. Ceratium Mrundinella, drawn in the living state, seen from the 



ventral surface, s, furrow in the cuirass. 

 Fig. 9. A Ceratium Mrundinella in which a part of the cuirass is deficient, 



drawn in the living state and seen from the ventral surface. 



pr, naked protoplasm j c, cuirass. 



XLII. — Critical Observations on Prof. Leidifs '■^Freshwater 

 RMzopods of North America,^'' and Classification of the 

 Rhizopods in general. By Surgeon-Major Wallich, M.D. 



[Continued from p. 334.] 



It has been already shown (' Annals,' Nov. 1885) that Prof. 

 Leidy does not dispute the fact of the animal of " Qiiadrula " 

 being in every respect identical with the animal of Diffliigia. 

 We must therefore not place too implicit credence in the 

 statement made at p. 143 of his work, that " Quadrula sym- 

 metrica is the only representative of its genus." For Prof. 

 Leidy has yet to explain upon what other basis than the 

 generic wow-identity of an organism with any other known 

 genus, he considers it legitimate to dissociate Difflugia sijm- 

 metrica from Diffiugia] and, further, how he can recon- 

 cile the creation of a new genus for the reception of that 

 form with those " investigations " which (he tells us at 

 p. 6) " rather confirm the view that we can only regard the 

 more conspicuous and prevailing forms as so many nominal 



