42 Reviews — Wachsmuth ^ Springer'' 8 Monograph on Crinoids. 



plates of the median series are strangely like arm-plates, both 

 in external view and in section, as I have figured in Pisocrinus 

 and Calceocrinus (" Crinoidea of Gotland ") ; in locrinus the median 

 series has an internal groove, similar to the ventral groove of the 

 right posterior arm, with which it coalesces in the superradial ; this 

 evidence, as well as the external folds of the plates, shows that the 

 median anal series of this and similar early forms was innervated 

 from the axial cord of the right posterior ray. 



These facts form an accumulation of evidence pointing in one 

 direction. Is there any a priori reason why the suggestion should 

 be rejected ? It is not so very startling. I have not maintained 

 that an arm-branch with its covering-plates and other organs was 

 metamorphosed into an anal tube. I have not even suggested 

 a change of essential function for the brachials themselves. The 

 function of brachials is to afford a flexible support to extra- 

 calycinal extensions of calycinal organs, and this is the function of 

 the mid-rib of the anal tube in locrinus. Why, I have asked, may 

 not the tegminal perisome become extended along an arm-branch 

 in the region adjoining the anus, just as we know that it is extended 

 in other regions ? We know that arms may become partly in- 

 corporated in the cup by a web-like extension of tegminal plates 



surfaces of E«, III on the left, bearing the median proximal anal, IV on the right, 

 bearing the first brachial ; in each are to be seen the dorsal ligament-fossa, two 

 muscle-plates and fossae, and a wide ventral groove merging into a narrow tongue 

 where the axial cord lay. These facts prove : (1) that r. post. Es was united to the 

 proximal anal in the same way as to IBr^ ; (2) that the anal mid-rib was innervated 

 by the same axial cord as was the r. post. arm. From which we infer (1) that the 

 proximal anal in locrinus actually is " a plate corresponding to an ordinary brachial " 

 in structure ; (2) that the mid-rib may have arisen as a branch of r. post, arm ; 

 (3) that, in any case, the application of the term axillare to r. post. Es in locrinus is 

 warranted by something more than the " angularity which occurs upon the upper 

 face," "the form of the plates succeeding it to the left, and the slanting position of 

 the posterior arm to the right" (W. & Sp., p. 129). 



Fig. 18. — Ossicles of locrimis, probably I. suhcrassus, in Mus. Comp. Zool. Harvard. 

 I. Eight posterior inferradial (Ei) and superradial (Es) and first primibrach 

 (IBri) seen from interior of cup. II. Upper articular surface of Ei ; groove on 

 left goes to X, that on right to brachials. III. Left upper articular surface of 

 Es, sup])ortiug x. IV. Eight upper articular surface of Es, supporting iBr^. 

 (Enlarged.) 



