Reviews — Wachsmuth i^ Springer's Monograj^h on Crinoich. 39 



higher position into the space between x and r. post. Es, and resting 

 on EA ; and, eventually, the retracing of these steps, accompanied 

 by grad'ual atrophy of all the anal plates. 



Now the present Monograph admits, as we have seen, the sinking 

 and re-raising of rt ; it also admits the sinking of the joroximal 

 median plate of the tube from its high position in Merocrinus and 

 Jocrinus to its low position in Heterocrinus and Ectenocrinus, and its 

 still lower position in Hybocrinus ; finally, it admits the sinking of 

 plate X from a level more than half its height above the radials, as 

 in JTomocrinus, to the level of the radials, as in CyatJiocrinus, and 

 its final expulsion from the cup. What it does not admit is the 

 possibility of a proximal tiibe-plate sinking down between the 

 radials so as to touch the basal. 



Thus the missing link in our chain of evidence is so slight, and 

 is of a nature so in accoi'dance with links that are known or 

 admitted, that we must demand some good reason for the refusal 

 to imagine this link and for the substitution of an entirely novel 

 postulate. The only tangible argument to be found in the 

 Monograph is given on p. 133, as follows : — "If it were true that 

 the plate of locriniis to the left of the supraradial [r. post. Es] 

 passed down in later forms to the basals, it would mean nothing 

 less than a partial revolution of the entire tube. This, however, 

 is disproved by the structure as well as the palaeontological develop- 

 ment of the tube, which latter is generally composed of longitudinal 

 rows of hexangular pieces, alternating in adjoining rows. In the 

 earlier and simpler forms the tube consists of only five series, one 

 to each interradius, that of the anal side resting upon plate t. 

 Later on, as the tube grew larger, a neio row of plates was 

 introduced ivith plate x supporting it. When there are three series, 

 as in Dendrocriinis, the third generally rests upon one side of the 

 left posterior radial. The arrangement of the plates within the 

 rows is so regular that if a sinking of the plate t had taken place 

 it would certainly be indicated by some disturbance among the 

 lower plates of the tube. In species where the tube has more than 

 three rows, one or more of the primary rows dichotomize at some 

 distance from the cup. [Compare Figs. 12 and 13.] The fact that 

 the increase of the tube phylogenetically took place by the intro- 

 duction of new rows of plates, is a strong argument in favour of 

 our idea that the plate x is also a supplementary piece, and was 

 introduced in the same manner as the plates which it supports." 



If the statement which I have italicized were " a fact," it would 

 be not merely "a strong argument," but absolute proof. But it is 

 merely another phrasing of the very idea that is to be proved ; and 

 it is a phrasing that emphasizes the difficulty, for it maintains that 

 the stout median line of the tube in locrinus and Merocrinus becomes 

 replaced by another stout median line in Homocrinus and Deudro- 

 crinus, and itself assumes a subsidiary position. No proof has yet 

 been given that the added series may not be those starting from 

 rt and It, rather than the two adjacent ones starting from x and It. 

 As for " disturbance," Wachsmuth and Springer's own interpretation 



