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



after death by liquefaction of tlie sarcode (L. N. 12, p. 6). This mistake is, however, easy to under- 

 stand, since in living Eadiolaria the calymma is usually invisible on account of its perfect 

 transparency, whilst in dead specimens it is usually quite distinct on account of the dust clinging 

 to its adhesive surface. I myself believed that the formation of the voluminous hyaline jelly-veU 

 was only partially due to liquefaction after death, but that it was to some extent present in the 

 living organism and that it might vanish and subsequently reappear by means of imbibition 

 (L. N. 16, pp. 109, 110). E. Hertwig was the first to demonstrate, in 1879, that the jelly-veil is 

 constantly present in living Eadiolaria, that it forms the basis of the extracapsular malacoma and 

 surrounds the central capsule as a second protective sheath (L. N. 33, p. 114). 



83. The Structure of the Calymma. — The extracapsular jelly -veil appears structure- 

 less in most Eadiolaria, inasmuch as it represents a homogeneous pellucid excretion of the 

 exoplasm and contains neither fibres nor other foi'med structures. In some groups, 

 however, definite structural characters become secondarily developed. The most common 

 and striking of these is the formation of alveoles, which takes place in the extracapsulum 

 (see § 86). In consequence of this the calymma assumes a remarkable frothy consist- 

 ency and appears to be composed of large, clear, thin-walled vesicles ; this is especially 

 the case in the Collodaria (Colloidea, Pis. 1,3, and Be lo idea. Pis. 2, 4), 

 and in many large Ph^odaria, especially among the Phasocystina (Phseodinida and 

 Cannorrhaphida, PI. 101, and Aulacanthida, Pis. 102-104). More rarely the calymma 

 is not permeated by vacuoles, but there appear in it fine strise parallel to the surface as 

 though it were composed of thin concentric laminse like an onion ; perhaps these are 

 the expressions of a difi"erent quantity of water in the various layers. In the calymma 

 of many Radiolaria thin, straight, radial lines are to be seen, which are probably pseudo- 

 podia, and not to be attributed to any structural modification, or they may be slender 

 canals which serve for the exit of the pseudopodia. On the outer surface of the calymma 

 of difi"erent Radiolaria, and especially in the Acantharia, a peculiar network of fibres 

 is to be found, composed of polygonal meshes, like elastic fibres, probably due to a 

 local thickening of the jelly. These polygonal meshes are often very regularly dis- 

 tributed between the radial spines of the Acanthometra, and stand in a definite 

 relation to them. The fibres which form the meshes are often rather strong, 

 resembling elastic fibres, as above-mentioned, and either simple or composed of bundles 

 of very fine fibrHlaj (L. N. 33, p. 15, Taf. i. fig. 1, Taf. ii. fig. 4). 



84. Hie Consistency of the Calymma. — The gelatinous material of which the 

 calymma of the Radiolaria consists is a pellucid mass, rich in water and usually quite 

 hyaline and structureless ; its consistency is very variable. In the majority of the 

 Radiolaria it may perhaps be about equal to that of the jelly which com23oses the 

 uml)rella of most Medusae ; but as in these latter it may vary between very wide 

 extremes, constituting on the one hand a very soft jelly-mantle, ofi"ering but little 



