CORRESPONDENCE. 201 



Lastly, observing that varieties among Foraminifera are of equal 

 value to species and even genera in higher animals, as far as concerns 

 bathymeti'ical and geographical distribution, I would refer the reader 

 to Dr. Carpenter's " Eesearches on the Foraminifera," ' Phil. Trans.' 

 for 1860, p. 584, &c., for valuable remarks on the Variability and 

 Persistence of Foraminifera. See also Ly ell's ' Antiquity of Man,' 

 4th edit., p. 494, &c. 



I am yoiu's truly, 



T. EuPEET Jones. 



P.S. — With regard to the spicular contents of Carpenteria and 

 Polytrema, mentioned at p. 65 (fifth line), Mr. H. J. Carter has 

 convinced himself by extended and close observation that the Sponge 

 spicules found in these Foraminifera have been chiefly taken in by the 

 sarcode during life, together with diatoms and other organic par- 

 ticles. In some instances the broken walls have allowed the entrance 

 of such strange bodies into the cavities ; and sometimes parasitic 

 Sponges wholly or partially invest the shells. Occasionally the 

 spicules are incorporated in the wall-tissue. Lastly, Mr. Carter 

 recognizes a close similarity in structure and features between Car- 

 penteria and Polytrema, leading him to combine the two under the 

 latter (older) name. See his memoir " On the PoJytremata," &c., 

 ' Ann. Mag. N. H.,' ser. 4, vol. xvii., March 1876, p. 185, &c., pi. 13. 

 — T. E. J., March 11, 1876. 



Chromatic and Spherical Aberration. 



To the Editor of the ' Monthly Microscopical Journal.' 



16, FiTZROY Square, W., JIarch 10, 1876. 



Sir, — In p. 232 of your November issue. Dr. Eoyston-Pigott 

 states that the spherical aberration of a monochromatic ray " is for 

 convenience called chromatic aberration," of which I maintain a 

 monochromatic ray to be destitute. 



In p. 129 of your last issue he admits that " in standard works on 

 Optics, chromatic aberration and spherical are treated for convenience 

 as distinct things." When we are in possession of Dr. Eoyston-Pigott's 

 " standard work on Optics," in which, I presume, these optical condi- 

 tions "will be treated as identical, "we shall be enabled to form an 

 opinion on the relative convenience of these very opposite modes of 

 treating the subject. 



In your February number he expresses a hope that I and others 

 who have addressed to you our dissent from his opinions, will on 

 further reflection regret having done so. I can only assure him that 

 I do not, nor am I likely to, regret this or any other steps that I 

 may have taken in furtherance of the logical accuracy of scientific 

 nomenclature. 



I remain yours faithfully, 



Chas. Bkooke. 



