and Affinities of Qraptolites. 369 



hydrocaulus is more or less constricted, or even provided with 

 an imperfect diaphragm, so that the hydrothecffi become proper 

 chambers, completely diiferentiated from the common perisarcal 

 tube (figs. 2 & 3). Now the calicles of the graptolite have 

 their cavity miinterruptedly continuous with that of the main 

 tube, there being no diaphragm or constriction of any kind at 

 the point where the one passes into the other (fig. 1)*. 



There is, however, another view of the calicles which will 

 meet this difficulty, a view suggested by the remarkable bodies 

 known as nematophores, and which are characteristic of the 

 Plumularidffi. These bodies constitute cup-like appendages 

 formed of chitine and filled with protoplasm, which has the 

 power of emitting pseudopodia or amoeboid prolongations of 

 its substance, and having their cavity in communication with 

 that of the common tube of the hydrocaulus. They present 

 two principal modifications, the movable and the fixed. In 

 the movable forms (fig. 2) the nematophore always springs 

 from a narrow point of attachment, whence it rapidly widens 

 towards the distal end, while its cavity is divided transversely 

 by an imperfect septum into two chambers. The nematophores 

 of this form are more or less movable on the narrow point of 

 attachment and are frequently caducous. They are charac- 

 teristic of the genera Pluvndaria proper, Antetintilaria, &c. 

 The fixed forms (fig. 3) commence with a wide basis of attach- 

 ment by which they are immovably fixed to the hydrocaulus ; 

 and they are usually, though not always, destitute of an in- 

 ternal septum. They are never caducous. These are charac- 

 teristic of such genera as Aglaophenia^ where (as is also the 

 case with the movable nematophores of other genera) they are 

 situated, some upon the median line, when they are necessarily 

 azygous, and some laterally, when they are in pairs. It is 

 more directly with these fixed forms that I would compare the 

 calicles of a graptolite ; and such a comparison will show how 

 exact is the resemblance. I have elsewhere shown that the 

 tooth -like processes which project from the edges of the hol- 

 low leaflets which form the walls of the corbula in Aglao- 

 'plienia (fig. 5, F, c) are bodies of an entirely similar kind ; and 

 the resemblance between these and the tooth-like processes of 

 many graptolites is complete. 



Now it is not alone in general form that the nematophores of 

 Aglaophenia resemble the calicles of a graptolite. The mode in 

 which their chitinous sheaths are seen to open into the common 



* M'Coy (' Brit. Pal. Foss.') speaks of a septum at the base of the cali- 

 cles in certain graptolites ; but subsequent observations ha\e not tended 

 to confirm this statement. 



