1532 THE VOYAGE OF H.M.S. CHALLENGER. 



of these interesting organs in living PH^EODARIA is required. Usually the sarcode, issuing 

 from the openings of the capsule, forms a stronger cylinder, with peculiar movements. 



The phseodium, or the peculiar dark extracapsular pigment-body of the PH^EODARIA, 

 is one of the most important and most characteristic parts of their organisation, 

 and has induced me to derive their name from it ; it is not less typical for the whole 

 legion, than the astropyle with its radiate operculum and the proboscis ; and both 

 these important parts are always in direct topographical and physiological connection. 

 Whilst I have missed the phseodium in no Ph&odarium in which the soft body 

 was well preserved, I have not found it in any other Radiolaria ; for the similar extra- 

 capsular pigment bodies, which are found in some species of Tlicdassicolla and some 

 other Sphserellaria, have a composition and signification different from that of 

 the phseodium an exclusive peculiarity of the PH^EODARIA. 



The typical importance of the phseodium for all members of this legion is proved 

 by the following five facts : (l) its constant presence in all PH^EODARIA ; (2) its 

 constant excentric position in the oral half of the calymma ; (3) its constant relation to 

 the astropyle, the operculum and the proboscis of which is always surrounded by it ; 

 (4) its constant considerable size, its volume being usually greater than that of the 

 central capsule, the aboral half of which is covered by it ; (5) its constant colour and 

 morphological as well as chemical composition. These five facts together demonstrate 

 by their absolute constancy the high morphological and physiological importance of 

 the phseodium for this peculiar subclass of Eadiolaria, although its true nature is 

 difficult to make out, and its main function is not yet sufficiently known. 



The first remarks that have been made on the phseodium were published in 1862 

 in my Monograph, where I noticed the peculiar dark brown extracapsular pigment 

 body and its excentric position covering only one-half of the central capsule, in Aula- 

 cantha (p. 263, Taf. ii. figs. 1, 2), in Thalassoplancta (p. 262, Taf. iii. fig. 10), and in 

 Caslodendrum (p. 361, Taf. xxxii. fig. 1). Its general presence and peculiar composition 

 were first recognised by Dr. John Murray, who had, during the Challenger Expedition, 

 the first opportunity of examining many big living PH^EODARIA brought up from great 

 depths. He gives in his first Report (1876, loc. tit., p. 536), the following important 

 notice : " The sarcode of all these deep-sea Rhizopods has many large black-brown 

 pigment-cells. Small bioplasts are scattered through the sarcode. These collect into 

 capsular-like clumps when the animal is at rest, and are quickly coloured by carmine." 

 In 1877 Dr. John Murray sent me the wonderful collection of PH^ODAEIA brought 

 home by the Challenger, and I had now the best opportunity for examining the 

 phseodium in hundreds of well-preserved specimens. Supported by these extensive 

 observations, I gave, in 1879, in a preliminary paper, 1 a fuller description of the 



1 Ueber die Pha;odarien, eine neue Gruppe kieselschaliger mariner Rhizopoden, Sitzungsb. med.-nat. Gesellsch. Jena, 

 December 12, 1879, pp. 3, 4. 



