THE ANNALS "^1 



AND 



MAGAZINE OF NATURAL HISTORY. 



[FOURTH SERIES.] 

 No. 14. FEBRUARY 1869. 



XV. — Observations on the Tlialassicollicla3. 

 By G. C. Wallich, M.D., F.L.S. 



The true value and significance of characters derived from tlie 

 degree of development of the sarcode-body of the Rhizopods, 

 as distinguished from those which are derived from their 

 mineral shells or skeletons, is perhaps nowhere more clear Ij 

 exemplified than amongst the families which I have asso- 

 ciated together in my second Order, namely the Protodermata, 

 which are characterized by the presence of a definite nucleus, 

 but are still not sufliciently difterentiated to exhibit the con- 

 tractile vesicle which appears, for the first time, amongst the 

 Actinophryan and Amoeban Rhizopods of the third Order, 

 namely the Proteina*. Thus, viewing their siliceous portions 

 apart from the animal body to which they afford support, it 

 would be difficult to point out structures exhibiting a smaller 

 amount of apparent resemblance ; and hence it is hardly a 

 matter for sm-prise that important differences of opinion should 

 have arisen concerning the true morphological relations of the 

 Polycystina, Thalassicollidte, and Acanthometrina, which con- 

 stitute the Rhizopoda Radiolaria of Miiller's system. But I 

 hope to be enabled to show that, however widely the mineral 

 framework may differ in the four groups constituting the Pro- 

 todermata, the uniform development and mode of disposition 

 of the sarcode-mass places their affinity beyond a doubt. 



The first accurate series of observations on the Thalassi- 

 collida3 was made by Huxley, and formed the subject of 

 an admirable paper contributed to tlie ' Annals and ]\Iaga- 

 zine of Natural History ' in 1851 (2nd ser. vol. viii. p. 483 

 et seqq.). With one or two unimportant exceptions, the 



* See a paper "On the Structure and Affinities of the Polycystina,"' 

 read before the Microscopical Society in May 1805, and published in tlie 

 August number of the ' Quarterly .Tournal of ^licroscopical Science.' 



Ann.d'Mag.N.lIist. Ser. 4. YoJ.Vu. 7 



