REPORT ON THE RADIOLARIA. xlvii 



A. The radial structure of the endoplasm was first described in my Monograph (18G2, p. 74), 

 though E. Hertwig (1879, p. 112) was the first to indicate its typical significance in the case of the 

 Peripylea, and to demonstrate its causal relation with the radial currents in the central capsule of 

 this legion. More recent investigations have led me to the conviction that this j)henomenon is more 

 widespread, and often more strongly developed, than was formerly imagined, and that it is probably 

 one of the typical characters of all Spumellaria (at least of the Monozoa). 



B. The centripetal cones of Pliysematium, which have hitherto been known only in these 

 colossal Thalassosphffirida, were fully described in my ilonograph under the name " conical centri- 

 petal cell-groups " ; by their first discoverer, A. Schneider (L. N. 13), they were termed " nests," 

 and compared with the " nests " (central capsules) of tlie Polycyttaria. In the Pliysematium 

 mulleri of the Meditteranean (hitherto only observed by Schneider and myself at Messina) it ap- 

 peared as though each centripetal cone were composed of a group of from three to nine (usually 

 four or five) slender wedge-shaped cells, whose common centripetal apex was produced into a 

 radial thread of sarcode (L. N. 16, p. 258, Taf. iii. fig. 7). Since then (1866) I have observed at 

 Lanzerote, in the Canary Islands, a nearly related form, which I take to be Pliysematium atlanticum, 

 Meyen. In this, however, the " centripetal cell-groups " were wanting, and the whole cortical layer 

 of the endoplasm was cleft into numerous radial portions, each enclosing a nucleus (probably the 

 mother-cells of flagellate sjDores, see p. 35). 



C. The radial fibres of the medullary endoplasm which cling to an extracted nucleus have been 

 observed by Hertwig in certain Sphreroidea {Diplosphoira, Arachnosphmra) (L. K 33, p. 40). 



78. The Endoplasm of the Actipylea. — The intracapsular protoplasm of the 

 AcANTHARiA or AcTiPYLEA is often distinguished by a partial or complete radial 

 arrangement like that of the Pekipylea, but differing in the number, size, form, and 

 distribution of the radial portions into which the endoplasm is diflerentiated. For since 

 the pores of the capsule membrane are distributed at equal distances all over the sur- 

 face in the Spdmellaria, whilst in the Acanthakia they are arranged in definite 

 groups, and since the number and arrangement of the pores has a direct influence ujjon 

 the internal currents of the endoplasm, it foUows that the radial structure in the latter 

 legion must be very different from that in the former. In addition to this there must 

 not be forgotten the important influence which the early centrogenous formation of the 

 skeletal rods exercises upon the disposition and growth of the intracapsular structures. 

 Hence the endoplasm of the Aoantharia does not separate into innumerable thin, 

 closely packed radial wedges or cortical radial rods, but into a small number of large 

 pyramidal portions between which run the radially disposed heterogeneous portions of 

 the contents of the capsule, viz., the radial bars of acanthin and the peculiar intra- 

 capsular " axial threads." As a direct consequence of the regular disposition of these 

 heterogeneous radial ^jortions, which is often characteristic of the various families of the 

 Acantharia, a corresponding diflerentiation of the endoplasm is brought about ; it 

 divides into a number of conical or pyramidal jjortions (radial pyramids), whose bases 

 rest upon the capsule -membrane and whose apices are directed towards the centre of 



