EEPOET ON THE BADIOLARIA. xxxix 



is commonly placed excentrically, and most usually in the apical or aboral portion of the 

 central capsule, either between its apex and the podoconus, or quite excentrically on the 

 dorsal aspect. The simple nucleus of the NASSELLARIA usually appears to be vesicular 

 and to possess a somewhat firm membrane, clear contents, and a rather large, dark 

 coloured nucleolus. In many NASSELLARIA the nucleus is spherical or ellipsoidal (PL 53, 

 fig. 11); whilst in many Stephoidea and Spyroidea, where the central capsule is 

 constricted by the sagittal ring and divided into two symmetrical lateral lobes, the 

 nucleus partakes of the same mode of growth, and appears in the middle of the capsule 

 as a transversely placed ellipsoid or even as a short cylinder (PL 90, figs. 7, 9), The 

 most remarkable modification in the form of the nucleus is to be found in the multi- 

 articulate Cyrtoidea. Here it is usually enclosed in the cephalis and is spherical, 

 ellipsoidal or spheroidal, often flattened almost into a disc. If now the central capsule 

 increase greatly in size and put forth three or four clavate lobes which hang down 

 through the pores of the cortinar septum into the thorax (or even into the succeeding 

 joints), the nucleus usually undergoes similar modification, and three or four finger-like 

 apophyses are developed from its base, which project into the corresponding lobes of the 

 central capsule (PL 59, figs. 4, 12, 13). 



The numerous small, spherical, homogeneous nuclei which are to be found in the central cap- 

 sules of those NASSELLARIA, which are ripe and about to develop spores, were described in 1862 in 

 my Monograph, as " numerous, small, transparent, spherical cells " in the case of various Cyrtoidea 

 (Arachnocorys, Lithomelissa, Eucecryphalus, JEucyrtidium, &c. (loc. cit., pp. 302, 305, 309, 321, &c.), and 

 I find them of the same form and dimensions, but deeply stained with carmine in many prepara- 

 tions in the Challenger collection. E. Hertwig has delineated them very accurately in the case 

 of Tridictyopus (1879, loc. cit., p. 84, Taf. vii. fig. 3). He was also the first to recognise the 

 uninucleate condition of the NASSELLARIA, which is much more frequently observed than the 

 serotinous multinucleate condition, and he described very clearly the peculiar lobed nuclei which 

 arise in Cyrtoidea, owing to the protrusion of the nucleus through the cortinar septum (loc. 

 cit, p. 85, Taf. viii. figs. 3-8). 



70. The Nucleus of the Cannopylea. The nucleus presents the same remarkable 

 structures in all species of the PH^EODARIA or CANNOPYLEA which have been examined, and 

 closely resembles the germinal vesicle of an amphibian ovum, being a large spherical 

 or spheroidal vesicle with numerous nucleoli. Its diameter usually amounts to half or 

 two-thirds, sometimes even three-quarters, that of the central capsule. The vertical 

 main axis of the latter is also that of the nucleus, which usually lies somewhat nearer to 

 the aboral pole. The nucleus is generally rather more strongly compressed in the direction 

 of the main axis than the capsule itself. The membrane of the vesicular nucleus is thin, 

 but firm, and encloses a clear or finely granular mass of nuclein. The number and size 

 of the contained nucleoli are variable even in one and the same species, and stand in 

 inverse ratio to each other, an obvious result of the gradual process of division. Commonly 



