EEPORT ON THE EADIOLARIA. vii 



nourishment of the Radiolaria, yet they are by no means indispensable to them. On the 

 other hand, the physiological individuality offers more complicated relations in the social 

 Radiolaria (Polycyttaria) which live united in colonies or coenobia. Here the actual 

 Bion (or the fully developed physiological individual) is not represented by the individual 

 cells, but by the whole multicellular ccenobium, which in each species has a definite form 

 and size. In these ccenobia, which are usually spherical or cylindrical jelly-like masses, 

 several millimeters in diameter, numerous cells are so intimately united that only their 

 medullary portions (the central capsule with the endoplasm) remain independent ; the 

 cortical portions (calymma and exoplasm) on the contrary uniting into a common extra- 

 capsulum. This discharges, as a whole, the functions of locomotion, sensation, and incep- 

 tion of nutriment, while the separate central capsules act in the main only as reproductive 

 organs (forming spores) and partly also as the central organs of metastasis (digestion). 

 Each ccenobium may also be regarded as a polycyttarium, i.e., a " multicellular Radio- 

 larian," whose numerous central capsules represent so many sporangia or spore-capsules. 



On this head compare the section in my monograph of 1862 (L. K 16), entitled Die Organisa- 

 tion der Badiolarien-Colonien ; Polyzoen oder Polycyttarien ? (pp. 116 to 126); and also E. Hertwig, 

 Zur Histologie der Eadiolarien, 1876 (L. 1ST. 26, p. 23). 



14. Monocyttaria and Polycyttaria. In the majority of the Radiolaria each 

 unicellular organism passes its individual life in an isolated condition (as a Mono- 

 cyttarium). Only in a part of the SPUMELLARIA numerous unicellular individuals are 

 united into societies which are regarded as cosnobia or colonies (Polycyttaria). This is 

 the case in three different families belonging to the PERIPYLEA, in the Collozoida (without 

 a skeleton, PL 3), the Spha3rozoida (with a Beloid skeleton, PL 4), and the Collos- 

 pha3rida (with a Sphasroid skeleton, Pis. 5-8). All three families of Polycyttaria (or 

 social Radiolaria), agree in their mode of forming colonies, since the central capsules of 

 the social individuals remain separate and lie in a common jelly-like mass, which is 

 formed by the fusion of their extracapsulum. The chief part of the voluminous 

 colonies, which attain a diameter of several millimetres (sometimes more than 1 cm.), and 

 are generally spherical, ellipsoidal or cylindrical, consists therefore of the jelly-like 

 calymma, and this is penetrated by a sarcoplegma, to whose meshes all the individual 

 organisms contribute by means of the pseudopodia, which radiate from their sarcomatrix. 

 A further peculiarity in which the social SPUMELLABIA differ from the solitary consists in 

 the fact that the former are precocious and the latter serotinous in the division of the 

 nucleus ( 64). Whilst in the solitary or monozootic SPUMELLAKIA the middle of the 

 central capsule is occupied by the simple nucleus, and this divides only at a late period 

 (immediately before the formation of spores) into the numerous spore nuclei, in the 

 colonial or polyzootic SPUMELLARIA this division takes place very early, and the middle 

 of each central capsule is usually occupied by an oil-globule. 



