CARADOCIAN CYSTIDEA FROM GIRVAK 379 



theca shows that, whatever the function of this organ, it cannot be anatomically 

 associated with the rectum. 



§ 68. It was M. Neumayr (1889, p. 407) who originally suggested that the 

 appendage was an arm, giving as his reasons, first, " its most striking resemblance to 

 the arms of Arachnocystites," secondly, " the extreme regularity of the doubled row of 

 pores . . . such as only obtains elsewhere in the case of ambulacral pores." This last 

 remark is explained by Neumayr's choice of an illustration : his fig. 107b is a reproduc- 

 tion of Barrande's pi. 26, f. 13, " montrant la trompe dans un etat de decomposition," 

 and apparently presenting an inner view of the plates with the transverse ridges 

 mentioned above (§ &6). There are no pores. 



§ 69. Haeckel (1896, p. 55), recognising Neumayr's error, reverted to the idea that 

 the appendage was a proboscis, perhaps with a distal mouth [which it has not], and 

 " probably surrrounded at its base by a circlet of uncalcified mouth-tentacles " [for 

 which there is no evidence whatever]. He also made the curious suggestion that this 

 appendage might be the stem, and that the stem (of Barrande) might be the proboscis. 

 In a review of Barrande's work in "Nature" (July 18, 1889, p. 269), I had already 

 pointed out the close resemblance of the " arms " of Arachnocystis and Dendrocystis to 

 the stem of the former, adding " one would almost imagine that they had originated in 

 the same manner," i.e. as gradual extensions of the theca. 



§ 70. Jaekel (1901, p. 673) merely says that the appendage "probably served for 

 the reception of the ambulacral organs." 



§71. In 1899 and 1900 (p. 48) I regarded this organ "as an extension from the 

 mouth, bearing a ciliated food-grove that could be closed by plates, and perhaps also 

 an extension from the water-ring." 



§ 72. It follows that there is a general consensus of opinion that the appendage is 

 connected with the subvective system. The ideas of " pores " and of a terminal 

 " mouth " being eliminated as inconsistent with the facts, the sole workable hypothesis 

 remaining is that the organ is essentially a brachiole, similar to those of Arachnocystis 

 and other Rhombifera, i.e. with two columns of stouter plates enclosing a groove, and 

 an alternating series of smaller plates that cover the same. It diff'ers from the usual 

 type in its less length, greater width, larger food-groove, and above all in its singleness. 

 This last feature will appear doubly peculiar when we realise that in the history of the 

 genus there is a gradual development of a process at the opposite angle of the theca, 

 clearly intended to counterbalance the appendage. If Dendrocystis were descended 

 from a normally erect form, in which exothecal skeletal supports for the subvective 

 system had already been evolved, we should be almost bound to suppose that those 

 processes must have been at least three, and possibly five, in number ; and we should 

 then find great difiiculty in understanding why they should not have been reduced to 

 two processes, as in so many genera of diverse origin but similar habit (e.g. Placocystis, 

 Pleurocystis, Comarocystis), the more so since two processes would have so naturally 

 supplied the " besoin " which, as Lamarck might have put it, the animal was struggling 



