10 Mindeskrift for J. Steenstrup. X. 



(textfig. 2). I have examined a specimen of a Trickaster in regard to these struc- 

 tures and must state definitely that they have nothing at all to do with pedicellariæ. 

 The part which Ludwig regards as the stalk of the "pedicellaria" is nothing but 

 thc side arm-plate. But that an adambulacral plate can never become the homo- 

 logue of a pedicellaria- stalk, be it ever so elongated and emancipated from the 

 corresponding ambulacral plate, needs no further discussion. 



On regarding the outer arm joints it is seen that there is a small rudiment of 

 a tentacular papilla (PI. I Figs 3 — 4); this papilla consists of a single rod, rising 

 from a nearly circular, fenestrated base. On the following joints it may be a little more 

 complicated, but it always remains vcry small. On thc fullgrown arm-joints there is 

 no trace of a tentacular papilla to be observed, hence they must be absorbed in 

 the course of growth. I have found the tentacular papilla to begin on the second 

 joint from the terminal plate in the four-armed specimen, while in the regenerating 

 arm from the other specimen they do not appear until the 6 — 7th joint. — The 

 tubefeet, which are closely set with sensory papiJlæ, as in Ophiothrix, issue 

 from the sides of the arm-joints. The quoted figure 3, PI. XI, of Bell 

 wrongly shows small tentacular pores at the outer edges of the ventral piates. In 

 that place no pores occur at all, and the real pores are of usual size, not so minute 

 as shown there. The same peculiar position of the tube- f eet obtains also in Ophiothela 

 (comp. PI. I Fig. 11), as well as in Ophiomaza and Ophiopsammium. 



As a main argument for the primitive character of Ophioteresis Bell emphasizes 

 the very simple structure of the vertebræ, which are stated to be "merely a gene- 

 ralized Ophiurid ossicle, without knobs or pits" (Op. cit. p. 179). The figure Bell 

 gives thereof, reproduced in textfigure 1, certainly gives this impression. In reality, 

 however, the primitive character holds good only for the figure. I have tried to give 

 some more accurate figures of the vertebræ of Ophioteresis, represented in PI. II. 

 figs. 1 — 7. I suppose that these figures will show convincingly that the typical knobs 

 and pits are really present and well developed. As usual there is on the aboral surface 

 a median knob with a pit at each side of it, and on the ad oral side correspondingly 

 a median pit with a knob at each side. (PI. II. figs. 1 — 2.). A comparison with 

 e. g. the figures 8 — 9, PI. II, representing the oral and aboral surfaces of the 

 vertebra of Ophiothrix fragilis shows that there is a complete accordance with regard 

 to the articulation between these two forms. The conspicuous difference otherwise 

 existing between them is due to the different development of the processes for the 

 attachment of the intervertebral muscles ; but the processes are the same in both, 

 and the depressions in them are the same; only the grade of their development 

 is somewhat different. — Accordingly Ophioteresis cannot on account of 

 its vertebral structure be regarded as in any way more primitive 



