Dr. Wallicli on tJie Rhizopods. 331 



vacuoles A vacuole was at times observed to gradually 



disappear; but it was doubtful whether any of these corre- 

 sponded with the contractile vesicle of other Rhizopods." He 

 then gives a very good description of the characters of the only 

 form of Gromia he had met with in North America, named by 

 him G.terricola^ partly on account of its habitat " in the crevices 

 of the pavement in the yard attached to his home in the city of 

 Philadelphia," and partly, I presume, owing to the animal 

 having a habit of accumulating at the posterior portion of its 

 test " more or less dirt consisting of fine granules and coarse 

 particles of quartz sand" (p. 280). But beyond this his 

 description of G. terricola would hold just as good for O. ovi- 

 formiSj or indeed any of the polymorphous varieties assumed 

 by these organisms, for it presents no new characters. 



The second erroneous statement I have to notice is even 

 more extraordinary than tlie former one, inasmuch as it does not 

 involve a misapprehension of my written opinions, but attributes 

 to me statements which are directly opposed to those really 

 made by me on the points in question. I allude to Prof. 

 Leidy's assertion in relation to Diffiugia symmetrica and the 

 entire series of new testaceous forms, of which, with three 

 before-mentioned exceptions, not one had been previously dis- 

 covered, so far as I am avrare, either in this country or 

 elsewhere, prior to the appearance of my paper " On the 

 Extent and some of the principal Causes of Structural Varia- 

 tion among the Difflugian Rhizopods," published in the 

 ' Annals ' for March 1864. 



At pp. 150 and 151 of his work Prof. Leidy says, " The 

 series of specimens represented by Dr. Wallich in tigs. 27 to 

 33, pi. xvi. of tlie 13tli vol. ' Annals & Mag. Nat. History ' 

 for 1864, and described as transition forms of Dijfflugia sym- 

 metrica, appear to me to pertain to the same animal as Nebela 

 collarisT 



It is not for me to hazard a conjecture how such a distorted 

 view of my clearly- expressed opinion regarding the tran- 

 sitional series of forma referred to could have been arrived at 

 by so careful an observer. At all events, I can positively 

 affirm that I never entertained or expressed such an opinion. 

 In all I wrote on the new varieties of the Diffiugidse I referred 

 only to the outwardly visible characters of the tests for reasons 

 already stated ; and neither directly nor indirectly described 

 " the specimens represented in my figures 27 to 33 of pi. xvi.," 

 as " transition forms of Diffiugia symmetrica.'''' What I did 

 state was that I considered them all as varieties of Diffiugia 

 proteiformis or its variety D. pyriformis ; and as such I 

 must continue to regard them until some much more satisfac- 



