REPORT ON THE RADIOLARIA. XXXVll 



wasserhelle Blaschen "). I was in error, however, in regarding the latter as identical with the 

 so-called " hyaline spherules " in the central capsule of many Monozoa, which rather belong to the 

 category of intracapsular vacuoles (see § 72). The credit of recognising, by the aid of the modern 

 methods of staining, the distinctness of these two structures, which may readily be mistaken for 

 each other, and of demonstrating the true nature both of the serotinous and precocious nuclei, 

 belongs to Richard Hertwig (1879, L. N. 33). 



68. The Nucleus of the Actipylea.— The nucleus of the Acantharia or Actipylea 

 shows very peculiar relations in respect of structure and division, particularly special 

 forms of lobular budding, which belong to the characteristic peculiarities of this singular 

 legion, and are not found among other Radiolaria. The position of the nucleus is alivays 

 excentric, even in the youngest Acantharia, for the centrogeneous formation of the 

 skeleton, the constant development of the earliest radial portions of it in the middle of the 

 central capsule, forces the nucleus from its normal central position. The majority of the 

 Acantharia, Hke most Polycyttaria, are precocious, the primary nucleus early dividing 

 into numerous small nuclei (see note A below). Nevertheless there are many exceptions 

 to this rule in different famiUes, e.g., Stauracantha, Xiphacantha, Phatnacantha, and 

 Pristacantha among the Acanthometra, and Stauraspis, Echinaspis, Dodecaspis, and 

 Phatnaspis among the A c a n t h o p h r a c t a. In these instances the primary nucleus 

 remains for a long time as a simple excentric ellipsoidal or irregularly round body, even 

 in the fully developed stage, and only at a very late period (sometimes just before the 

 formation of the spores) divides into many small nuclei. Since this serotinous division 

 of the nucleus takes place in diflerent genera of very various groups, it can only be decided 

 by further investigations how widely it is spread among the Acantharia, and upon what 

 circumstances it is dependent (see note B). The division of the nucleus appears to be 

 precocious in the majority of this legion, and a number of small nuclei appear to be 

 early formed by a peculiar process of budding ; in most fully developed Acantharia 

 these are disposed in one or two layers under the surface of the central capsule, but if 

 their numbers increase to any considerable extent, the whole space between the skeletal 

 rods becomes filled with small nuclei ; sometimes these are homogeneous, sometimes 

 vesicular, 0-002 to 0'012 mm. in diameter; usually they are spherical and have a small 

 nucleolus (compare PI. 129, figs. 6-11, and note C). 



A. The numerous nuclei, which are to be found in the central capsule of most mature 

 Acantharia, were first described in my Monograph (1862) as " spherical, transparent vesicles, 

 provided with a small dark granule " (p. 374, Taf. xv. figs. 2, 5 ; Taf. xvi. figs. 2, 4; Taf. xxi. fig. 7, &c.). 

 Their more minute constitution and pecuHar origin were first accurately delineated by E. Hertwig 

 (1879, he. cit, pp. 11-24, Taf. i-iii.). 



B. The fact that in a number of Acantharia the nucleus does not divide early as in the 

 majority of the legion, but only at a later period, was first observed by R. Hertwig in a species of 

 Acanthometra {Xipliacantha scrrata), and a species of Acanthophracta {Phatnaspis 



