vi THE VOYAGE OF H.M.S. CHALLENGER. 



the case is the more necessary, inasmuch as the early division of the nucleus has no 

 further influence upon the organisation. Just us in many other classes of the Protista 

 there are monozootic (solitary) and polyzootic (social) forms, so also in the Radiolaria there 

 are in addition to the ordinary monozootic or monobious forms certain families in which 

 colonies or ccenobia are formed by the association of individuals ; this distinction may be 

 expressed by the terms " Monocyttaria " and " Polycyttaria." 



The unicellular nature of the Eadiolaria was first established by Eichard Hertwig in 1879 

 (L. N. 33), 1 and brought into conformity with our present histiological knowledge and the new reform 

 of the cell-theory. Huxley, however, who was in 1851 the first to examine living Eadiolaria 

 accurately, declared Fhalassicolla nucleata to be a unicellular Protozoon, and the individual central 

 capsules of Sphcerozoum punctatum to be cells, but, owing to the then condition of the cell-theory, 

 he was unable to give a conclusive demonstration of this view. Later, when Johannes Miiller in 

 1858 and myself in 1862 recognised the peculiar " yellow cells " which occur in large numbers in 

 many Eadiolaria as true nucleated cells, it appeared impossible any longer to maintain the unicellu- 

 lar nature of the Eadiolaria ; also the great complication which I showed to exist in the structure 

 of Thalassicotta appeared to contradict it. Only after Cienkowski (1871) and Brandt (1881) had 

 shown that the " yellow cells " do not belong to the Eadiolarian organism, but are symbiotic uni- 

 cellular algae, was it possible to revive and demonstrate anew the unicellular nature of the Eadiolaria. 



12. Morphological Individuality. From the morphological standpoint the indivi- 

 duality of the unicellular elementary organism is obvious in the ordinary solitary 

 Radiolaria (Monobia), and is to be so regarded that the whole body with all its 

 constituent parts, and not merely the central capsule, is to be regarded as a cell. 

 Naturally the xanthellse or yellow cells ( 76, 90), which as independent algse live in 

 symbiosis with many Radiolaria, must be excluded. The unicellular organisation of the 

 Radiolaria is further to be distinguished from that of the other Protista, inasmuch as 

 an internal membrane (capsule-membrane) separates the central (medullary) from the 

 peripheral (cortical) portion. In the ccenobia of the social Radiolaria (or Polycyttaria), 

 the morphological individuality persists only as regards the medullary portions of the 

 aggregated cells (the individual central capsules), while the cortical portions fuse com- 

 pletely to form a common extracapsulum. Hence in these SPUMELLAEIA polyzoa two 

 different stages of morphological individuality must be distinguished, the Cell as a 

 Morphon of the first stage, and the Ccenobium as a Morphon of the second stage. 



13. Physiological Individuality. From the physiological standpoint also the indi- 

 viduality of the unicellular organism is immediately obvious in the case of the ordinary 

 solitary Radiolaria (Monobia) ; as in other Protista it fulfils all the functions of life by 

 itself alone. This physiological individuality of the monobious Radiolarian cell is further- 

 more not influenced by the xanthellae, which live as independent algae in symbiosis with 

 many Radiolaria ; even though these often by the production of starch assist in the 



1 The numbers preceded by L. N. refer to the list of names of authors in the Bibliography on p. clxxvi. 



