REPORT ON THE RADIOLARIA. xHx 



undergone by the form and contents of the central capsule in the different groups of 

 MoNOPYLEA, especially those due to the formation of the skeleton, are not without 

 influence upon the podoconus. The most important divergencies from the above 

 described primary form are the following : — (l) The vertical axial cone becomes oblique, 

 its axis inclining in the sagittal plane and approaching either the dorsal or the ventral 

 wall of the capsule ; the cause of this appears to be usually the excentric development 

 of the growing nucleus or the formation of a large oil-globule. (2) The smooth mantle 

 of the podoconus becomes divided by three longitudinal furrows into three equal pro- 

 minent ridges, which correspond to three circular lobes in the porochora ; the cause of 

 this basal triradial lobular formation lies probably in the triradial development of the 

 skeleton in many Nassellaria or in the cortinar structure of the coUar septum. (3) 

 The simple podoconus splits into three or four elongated lobes, which eventually become 

 almost completely separated and correspond to the lobes of the central capsule, in the 

 axial wall of which they lie as longitudinally striated bands. The behaviour of these 

 bands justifies the hypothesis that the podoconus is a muscular differentiated portion of 

 the endoplasm and is composed of myophane fibrillse, whose contraction determines the 

 opening of the central capsule. 



A. The podoconus of the Monopylea was first described by R Hertwig in 1879, and recognised 

 as a characteristic component of the central capsule in the most various groups of this legion (in 

 Plectoidea, Stephoidea, Spyroidea, and Cyrtoidea; see his figures, loc. cit., Taf. 

 vii., viii., and the description, pp. 71, 73, 83, 106). Hertwig called it the " pseudopodial cone," and 

 regarded it as a conical process of the capsule-membrane, which is developed from this latter and 

 projects from the porous area into the interior of the central capsule; "it is penetrated by fine canals 

 which arise at the apex of the cone, diverge towards the base, and terminate there in the rods of the 

 pseudopodial area. The intracapsular protoplasm penetrates at the apex of the pseudopodial cone 

 into its fine canals, runs along them and emerges from the rods of the porous area in the form of 

 slender threads" {loc. cit., p. 19). I cannot agree with this view of Hertwig, although I have been 

 able to confirm the accuracy of his description by my own observations upon numerous excellently 

 stained and preserved prejjarations in the Challenger collection. As I have proved by numerous 

 teased out preparations, and as Hertwig himself correctly states, " the cone is more readily detached 

 from the membrane than from the protoplasm, when the capsule is teased " {loc. cit., p. 73). Hence 

 I regard the podoconus not as a differentiated portion of the capsule-membrane but as endoplasm, 

 and believe that it is composed of myophanes or " contractile muscular fibrils " in the same manner 

 as the cortical layer of the Cannopylea. Probably the contraction of these fibrils serves to raise the 

 opercular rods and hence to allow the exit of the endoplasm through the pores which lie between 

 these opercular rhabdillae (compare § 59). 



80. Tlie Endoplasm of the Cannopylea. — The intracapsular protoplasm of the 

 Ph^odaria or Cannopylea is distinguished from that of the other three legions by 

 several characteristic peculiarities, which are very important, since they stand in causal 

 relation to the typical structure of the capsule-membrane and in particular of its 



(ZOOL. CHALL. EXP. — PART XL. — 1886.) Er gr 



