Dr. Wallich on the EMzopods. 



463 



That any real disregard for accuracy was manifest in em- 

 ploying the specific name symmetrica I deny, for if such hyper- 

 critical accuracy were indispensable in treating of such organ- 

 isms as the tests of the Ehizopods, some of Prof. Leidy's 

 statements, such, for example, as that about the " chitiuoid 

 membrane," would, I fancy, not fail to invoke some rather 

 more hypercritical. But, apart from this, I maintain that 

 every one of the specimens I have ever seen indicates all 

 that is needed to justify the term symmetrica^ inasmuch as 

 tendency towards a definite and symmetrical arrangement is 

 perfectly clear, the deviation from symmetry being obviously 

 the result of accident rather than inherent tendency. And 

 we must not ignore the fact, for it is a fact, that the cases are 

 almost always exceptional in the organic world in which per- 

 fect symmetry is observable, the honeycomb being one of the 

 most familiar examples. But what then ? The bee is only 

 the tool working out a figure which is controlled and directed 

 by other physical forces and tendencies than those that are 

 inherent in it. And so it is, I contend, with those ^' thin 

 square plates of chitinoid membrane," which nevertheless 

 happen to be silicious and able to withstand heated acids. 



The two figures here given of Diffiugia symmetrica, though 

 somewhat roughly drawn, 

 are nevertheless sufficiently Fig- 1- 



accurate representations of 

 the specimens from which 

 they were taken. In the 

 larger test it was my desire 

 to show how accidentally 

 applied disturbing causes, 

 whether operating from with- 

 out, or disturbance caused 

 by the pseudopodia or chi- 

 tinosarc of the animal, may 

 occasionally break the regu- 

 larity of the serial order of 

 the plates. In no specimen 

 have I ever seen a truncate angle ] and where there has been 

 any overlapping of plates its character has plainly pointed to 

 disturbance of some sort acting from without. Both figures, 

 I venture to think, inculcate this lesson. The three separate 

 plates convey a fairly correct idea of their symmetrical form. 



At p. 151 of his work Prof. Leidy says : — " Dr. Wallich, 

 referring to the structure of the transitional forms of Diffiugia 

 symmetrica, which, as previously intimated, I suspect to 



