REPORT ON THE RADIOLARIA. cxxxix 



The sexual differentiation of the Polycyttaria was first discovered in 1875 by B. Hertwig, and 

 accurately described in the case of Collozoum inerme as occurring in addition to the formation of 

 the ordinary crystal-spores (L. N". 26, p. 36) ; compare also the general discussion of Biitschli 

 (L. N. 41, p. 52). Eecently Karl Brandt has demonstrated the formation of both homogeneous 

 isospores (crystal-spores) and heterogeneous anisospores (macro- and microspores) in seven different 

 species of Polycyttaria, and has come to the conclusion that in all social Eadiolaria there is a regular 

 alternation between the former and latter generations. Compare his elaborate account of the 

 colonial Eadiolaria of the Gulf of Naples (L. K 52, pp. 145-178). 



217. Inheritance. Inheritance is to be regarded as the most important accom- 

 paniment to the function of reproduction, and especially in the present case, because 

 the comparative morphology of the Radiolaria furnishes abundant instances of the 

 action of its different laws. The laws of conservative inheritance are illustrated by the 

 comparative anatomy of the larger groups ; thus, in the four legions the characteristic 

 peculiarities of the central capsule are maintained unaltered in consequence of continuous 

 inheritance, although great varieties appear in the skeleton in each legion. The 

 individual parts of the skeleton furnish by their development on the one hand and their 

 degeneration on the other, especially in the smaller groups, examples of progressive 

 inheritance. Thus in the SPUMELLARIA the constant formation of the primary lattice- 

 shell (a central medullary shell) and its ontogenetic relation to the secondary one, which 

 is developed concentrically round it ; can only be explained phylogenetically by 

 conservative inheritance, whilst on the other hand the characteristic differentiation of 

 the axes in the various families of the SPUMELLARIA is to be explained by progressive 

 inheritance. In the ACANTHARIA the arrangement of the twenty radial spines (in 

 accordance with Miiller's law, 110, 172) was first acquired by a group of the most 

 archaic Actinelida (Adelacantha) through hydrostatic adaptation, and has since 

 been transmitted by inheritance to all the other families of the legion (Icosacantha). The 

 morphology of the NASSELLARIA is not less interesting, because here several different 

 heritable elements (the primary sagittal ring and the basal tripod) combine in the most 

 manifold ways in the formation of the skeleton (compare 123, 124, 182). The affinities 

 of the genera in the different families yield an astonishing variety of interesting 

 morphological phenomena, which can only be explained by progressive inheritance. 

 The same is true also of the PH^ODARIA. In this legion the primary inheritance is 

 especially manifested in the constant and firm structure of the central capsule with its 

 characteristic double wall and astropyle, whilst the formation of the skeleton in this 

 legion proceeds in different directions by means of divergent adaptation. The 

 morphology of the Radiolaria thus proves itself a rich source of materials for the physio- 

 logical study of adaptation and inheritance. 



