182 PROF. ST. GEORGE MIYAET ON T^"^ 



larians have no capsule at all, a coudition wliich seems indicated 

 bj Sir C. Wy ville Thomson *. 



In spite, however, of these latter considerations, I am inclined, 

 on the strength of the distinctions above enumerated, to keep 

 provisionally apart, as two equivalent and divergent groups, the 

 Heliozoa and the liadiolaria. 



As to the unicellular nature of Eadiolarians, the most recent 

 researches of Hertwig have convinced him that however diverse 

 may be the contents of the capsule, they are nevertheless only 

 the products of the differentiation of a single cell, such as we 

 find in many small animals and in plants, which are admitted to 

 be unicellular. 



The yellow cells, however, stand markedly apart ; and if Hert- 

 wig is right in his views respecting them, then those true cells 

 must take their rise in a multinucleate sarcode as a true endoge- 

 nous cell-formation — a rare occurrence. 



If, however, the yellow cells should turn out to be parasitic 

 organisms, they will not only thus cease to be mysterious, but 

 the circumstances will render the truly cellular nature of the 

 " centripetal cell-groups " of Pliysematium more improbable, seeing 

 that they will then be the only instance of true cells in the Ea- 

 diolaria, and thus the existence of some error of observation in 

 this regard will seem more probable. 



If Hertwig is right in his view as to the origin of the nuclei of 

 ThaJassicolla, then we have therein a mode of origin elsewhere un- 

 known amongst animals, viz. nucleoli dividing, passing out from 

 the nucleus, and becoming nuclei themselves. The author's pre- 

 vious observations t as to nuclei would appear to make his theory 

 less improbable; but it should be duly noted that Professor W. 

 Flemming disputes J Hertwig's views. 



Without venturing to express an opinion in this controversy, I 

 would place on record that Hertwig has come to the conclusion 

 that a multinucleolate cell is potentially multinucleate, as a mul- 

 tinucleate cell is potentially multicellular; and thus we get a 



* His words are: — "In many Eadiolarians, and especially in some very pecu- 

 liar compound forms, a spherical internal chamber, called the ' central capsule,' 

 whose function we do not fully understand, is very prominent. This capsule is, 

 however, absent, or at all events exists in a very modified form, in the more typi- 

 cal groups." — ' Voyage of the Challenger,' vol. i. p. 232. 



t 'Morphol. Jahrbuch,' vol. ii. p. 63, pi. iii. 



I Archiv f. mikrosk. Anat. vol. xiii. 1877, p. 692, pi. xlii. 



