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



fig. 2), or only an incomplete Beloid skeleton (Canuorrliaphida, PI. 101, figs. 3, G, and 

 Aulacanthida, PI. 104, figs. 1-3). The Phaeosphseria also (Aulosphserida, 

 Ccelacantliida) and the P h se o g r o m i a (Tuscarorida, Challengerida) appear sometimes 

 to divide ; at all events, their central capsule often contains two nuclei. Of special 

 interest is the spontaneous division of the P h se o c o n c h i a, especially the Concharida 

 (PI. 124, fig. 6). In all monozootic Radiolaria, the nucleus first divides by a median 

 constriction into two equal halves (usually by the mode of direct division) ; then the 

 central capsule becomes constricted in the middle (in the Ph.^odaria in the vertical 

 main axis), and each portion of the cajisule retains its own nucleus. In the P h se o- 

 c n c h i a each half or daughter-cell corresponds to one valve of the shell, dorsal or 

 ventral, so that probably on subsequent separation each daughter-cell retains one valve 

 of the mother-cell, and forms a new one for itself by regeneration (as in the Diatoms). 

 In the pol}^zootic Radiolaria, which already contain many small nuclei, but usually 

 only a single central oil-globule in each central capsule, the division of the latter is 

 preceded by that of the oil-globule. In many Polycyttaria the colony as a whole 

 multiplies by division". 



The increase of the central capsule by division was first described in 1862 in my Monograph 

 (L. N. 16, p. 146) ; since then E. Hertwig (L. N. 26, p. 24) and K. Brandt (L. N. 52, p. 144) have con- 

 firmed my statement. In the Ph^eodaeia the division of the central capsule appears always to 

 take place in the main axis ; in the bilateral sometimes in the sagittal, sometimes in the frontal 

 plane. In the Tripylea each daughter-cell seems to retain one parapyle and half the astropyle 

 (compare the general descrijition of the Ph.^gdaeia, PL 101, figs. 1-6, PI. 104, figs. 1-3, and also 

 Hertwig, L. N. 33, p. 100, Taf. s. figs. 2, 11). Eegarding the spontaneous division of colonies of 

 the Polycyttaria, see K. Brandt, L. K 52, p. 142. 



214. Cell-Gemmation. — Reproduction by gemmation has hitherto been observed 

 only in the social Radiolaria, but in them it appears to be widely distributed, and 

 in very young colonies is perhaps almost universally present. The gemmules or 

 capsular buds (hitherto described as "extracapsular bodies") are developed on the 

 surface of young central capsules before these had secreted a membrane. They grow 

 usually in considerable numl^ers, from the surface of the central capsule, which is some- 

 times quite covered with them. Each bud usually contains a raspberry-like bunch of 

 shining fatty globules, and by means of reagents a few larger or a considerable number 

 of smaller nuclei may be recognised in them ; the naked protoplasmic body of the bud is 

 not enclosed by any membrane. As soon as the buds have reached a certain size they 

 are constricted ofi" from the central capsule and separated from it, being distributed in 

 the meshes of the sarcoplegma by the currents in the exoplasm. Afterwards each 

 bud becomes developed into a complete central capsule by surrounding itself wdth 

 a membrane when it has attained a definite size. From the special relations of 

 the processes of nuclear formation, which take place in the multiplication of the 



