Inter-relations of the Classes of the Echinodermato. 207 



flic groups of the Ecliinozoa anioiii^ themselves? Arc some 

 of the so-called Cysticlea nearer to (Jriiioids than others arc to 

 Echinoids? Unless the Holothurians are primitive forms, 

 how is one to imagine the means by which tliey reacquired 

 their primitive (or more worm-like) characters? The 

 " Cystids " are undoubtedly primitive, and yet how can that 

 condition be shown in any scheme of classification which 

 separates them from the Holothurians? And, finally, how 

 with current views, can one draw up exact, consistent, and 

 inclusive diagnoses? 



Forced by considerations of this kind to examine afresh 

 the classification of p]chinoderms, I have been led to some 

 conclusions which I should like to have an opportunity of 

 putting- — and 1 will do it as concisely as I can — before those 

 who are interested in questions of this kind. In the pre])a- 

 ration of my notes I have been greatly aided by the know- 

 ledge and criticism of my colleagues, Mr. F. A. Bather and 

 Mr. J. Walter Gregory, of the Geological Department of the 

 British Museum, which have been freely extended to me ; 

 various faults, both of omission and commission, have in 

 consequence been avoided ; for such as remain in this paper 1 

 must ask to be alone responsible. 



In what follows I do not propose to cite to any extent 

 the names of those numerous writers who have in the last 

 decade reopened various questions in the systematic or 

 phylogenetic classification of the Echinodermata ; for the facts 

 with which I am going to try and defend what is new in the 

 classification to be proposed are all perfectly well known. It 

 is only in the way of looking at them that there is, I imagine, 

 anything novel. 



(a) The Relation of the Holothurioidea to the rest of the 

 Echinodermata. 



The following characters seem to be of weight : — 



1. There is no system of plates corresponding to those that 

 form the " calycinal area " in other Echinoderms ; hence the 

 group may be said to be non-caliculate. 



2. The genital apparatus is not disposed quinqueradially ; 

 in all other Echinoderms the gonads are either arranged along 

 the rays or, when they fuse, in the interradii — they may, in 

 a word, be said to be actinogonidiate, whereas the Holo- 

 thurian, with its bilaterally symmetrical or asymmetrical 

 gonad, is anactinogonidiate. 



These two characters appear to me to be of very great 



