REPORT ON THE RADIOLARIA. 29 



latter. It seems to be merely a consequence of this diftereuce that the cleavage of 

 the nucleus commonly takes place very late in the former, very early in the latter. 



Commonly, therefore, the full-grown Thalassosphserida (until immediately before 

 their propagation) exhiljit one single nucleus in the centre of the capsule, whilst 

 in the Sphaerozoida the capsule is distended with numerous small nuclei. In these 

 latter the centre of the capsule usually contains one large oil-globule, whilst in the 

 former oil-globules are either wanting or scattered in large numbers in the endoplasm, 

 or disposed in one layer on the inside of the capsule membrane. 



In the solitary Thalassosphaerida each capsule is enclosed in its own peculiar 

 spherical calymma, whilst in the associated Sphserozoida all the capsules of the colony 

 are united into one common, very voluminous, alveolated calymma. 



Family III. Thalassosph.erida, Haeckel, 1862, (PI. 2). 

 Thalassosphcerida, Monogr. d. Radiol., p 25.5. 

 Definition. — B e 1 o i d e a solitaria. 



The family Thalassosphserida comprises all solitary Spumellaria with an imper- 

 fect skeleton, composed of numerous solid needles or spicula, scattered around the 

 central capsule in the calymma. The structure of the unicellular soft body is quite the 

 same as in the ThalassicoUida ; it differs from these only in the possession of the extra- 

 capsular skeleton. All needles of this skeleton are solid siliceous spicula, never hollow, 

 as in the similar Cannorhaphida among the Ph.eodaria. In the special structure and 

 form of the skeleton the Thalassosphserida agree perfectly with the well-known, colony- 

 building Sphserozoida ; they differ from these only by their hermit-like life and by some 

 peculiarities derived from this solitary development. 



The oldest known form of this family is probably the first Radiolarian, observed in 

 the living state, described in 1834 liy Meyen as Physematium atlanticum (see p. 35). 

 A second form was figured in my Monograph (1862) as Thalassosphmxi hifurca (p. 260, 

 Taf. xii. fig. 1). A third form was there described under the name TJialassospJuera 

 inofum ; this remarkable form was first observed by Johannes Mliller, and figured under 

 the name TJicdassicoUa morum (1858, Abhandl, p. 28, Taf. vii. figs. 1, 2). The same 

 form was afterwards observed living by myself in the Mediterranean, as well as in the 

 Atlantic, and in great numbers l)y the late Sir AVyville Thomson in the Pacific. The 

 latter gave a good figure of it with some valuable remarks in his excellent work. The 

 Atlantic (1877, vol. i. p. 233, fig. 51). He called this peculiar Rhizopod Calcaromma 

 calcarea, on account of the very peculiar calcareous bodies " looking in outline like the 

 rowels of spurs," which are accumulated in great quantity around the central capsule, in 

 the calymma. Further investigations have convinced me that these peculiar stellate 



