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



which each of the two daughter-cells develops to a complete mother-cell depends upon 

 simple growth. Another form of regeneration, different from this, has been observed in 

 Thalassicolla. If the central capsule be extracted artificially from the large concentric 

 calymma, the enucleated central capsule produces a new extracapsulum, with sarcoma trix, 

 pseudopodia, and calymma. This experiment may be repeated several times with the 

 same result. (Compare A. Schneider, 1867, L. N. 20.) 



152. The Formation of Colonies. The individual development of colonies takes 

 place in all three families of the Polycyttaria (Collozoida, Sphserozoida, Collosphaerida) 

 in the same simple way, by the repeated division of a single monozootic SPUMELLARIAN. 

 Since these divisions only affect the central capsule and not the extracapsulum, the 

 sister-cells, which arise by repeated division of the mother, remain enclosed in a common 

 rapidly growing calymma. Probably in all Polycyttaria the commencement of the 

 formation of colonies immediately follows the ^Ic^'ssa-stage of the monozootic mother- 

 cell (or takes place in the Thalassicolla-stage, which arises from the former by the 

 development of alveoles in the calymma). The simple central nucleus separates (by 

 direct nuclear division) into two halves, and the central capsule follows this process of 

 bisection, becoming constricted in the middle between the two daughter nuclei (PI. 3, 

 fig. 12). In the further growth of the colony the process of division proceeds in the 

 older, now multinucleate, central capsules, in which an oil-globule has taken the place of the 

 original nucleus ; then the division of the oil-globules precedes that of the central capsule 

 (PI. 5, fig. l). Another mode of growth of the colonies is the multiplication of the 

 central capsules by gemmulation, or the formation of the so-called " extracapsular 

 bodies" (Gemmulse, 214). The characteristic skeletal structure of the different species 

 appears at a later stage. Whether ripe central capsules can emerge from the social 

 bond of a coenobium, and, having become isolated, establish the formation of a new colony, 

 is very doubtful. The various forms which the ccenobium assumes in the different species 

 of Polycyttaria, are due partly to simple growth, partly to the development of large 

 vacuoles in the calymma. 



The form and size of the ccenobia appear in many fully developed Polycyttaria to exhibit specific 

 differences, which require further investigation ; in the young stage, on the contrary, they are simple 

 spheres or ellipsoids, often cylindrical .or sausage-shaped (PL 3, figs. 1, 4, 6, 11). In some species 

 the cylindrical gelatinous bodies become moniliform, and separated by transverse constrictions into 

 many segments, each of which encloses a large alveole (PI. 3, fig. 10). The rare ring-shape 

 (PI. 4, fig. 1) which I figured in 1862 in the case of Collozoum (L. N. 16, p. 522, Taf. xxxv. fig. 1), 

 I have recently observed in different species of Polycyttaria ; it is capable of a very simple mechanical 

 explanation, both ends of a sausage-shaped colony having been accidentally brought into contact 

 by a wave and having united by agglutination. Quite recently Brandt has given a very complete 

 account of the development, form, and growth of Polycyttarian colonies in his work on the colonial 

 Radiolaria of the Bay of Naples (1885, L. N. 52, pp. 71-85). 



