j 2 ECHINOIDEA. II. 



which may throw any light on the subject . But the study of pedicellariae has only added a new 

 factor differing in no way in its potentiality from those formerly in use , and there are several diffi- 

 culties to their use in classification. Like the other characters employed to distinguish the species 

 they vary with age. They form no exception and do not appear fully fledged in the embryos and 

 young specimens, in spite of Dr. Mortensen's statement to the contrary; though he acknowledges that 

 there is in literature next to no more exact accounts of the development of the pedicellariae of Echi- 

 noids. Certainly before making such a sweeping use of the minute and often infinitesimal characters 

 supplied by pedicellariae for classification it would have been instructive to trace the development of 

 the several kinds of pedicellariae, and obtain some data regarding the extent and nature of the vari- 

 ation of pedicellariae during their growth. The only addition made by Dr. Mortensen to our know- 

 ledge of the development of pedicellariae is shown on Figs. 15, 24, 30 PI. XII of the Ingolf Echinoidea, 

 giving three stages of a triphy lions pedicellaria of Phormosoma placenta. As long as we know so little 

 regarding the nature of the relations of the large and the small pedicellariae of the same kind to one 

 another it seem useless to speculate on the improbability ... of the arrangements which must take 

 place in the calcareous mass to make a small fully formed pedicellaria become a larger one . Every 

 student of Echini is fully aware of the immense amount of resorption and rearrangement constantly 

 taking place in the actinal and abactinal parts of the coronal plates in the interambulacral areas, and 

 in the actinal and abactinal systems — changes that are far greater than those referred to above can 

 be . — Further Professor Agassi/, quotes my remark (p. 9): When no pronounced difference is found 

 between large and small pedicellariae, it may in fact be impossible to decide whether a certain speci- 

 men is to be regarded as a large or small form and adds that surely this acknowledgement that 

 the pedicellariae cannot be classified may throw some doubt on the statement that the pedicellariae 

 give absolutely excellent systematic characters (p. 106 — 7). 



In reply to these objections I cannot do better than refer to the remarks of Professor Doderleiu 

 (Op. cit. p. 67— 721. In a way that could scarcely be better or clearer the whole question is discussed 

 there, and with full conviction I can subscribe to every word of it. < )nly a few remarks may be added. 

 I want to state explicitly that I quite agree with the remark that the new factor (the pedicellariae) 

 differs in no way in its potentialitv from those formerly in use ; it can never be said beforehand with 

 certainty whether the pedicellariae — or any other factor -- are of primary importance in some group 

 or not, only a careful comparative study can show the relative value of the different structural cha- 

 racters. I have never stated that the classification lias always to be based on the pedicellariae as the 

 most important factor; on the contrary, I am of opinion that where structural characters of some 

 significance occur in the test, these are upon the whole of higher classificatory value than the cha- 

 racters in the pedicellariae. — The assertion that the pedicellariae do not appear fully fledged in the 

 embryos and young specimens in spite of Dr. M.'s statement to the contrary is quite unjustified. My 

 statement is not founded on the accounts thereof in literature but on my own fairly extensive studies; 

 and I would remark that I do not speak of the embryos in this connection but of the newly meta- 

 morphosed Echinoid (p. 7). All the different kinds of pedicellariae may not perhaps be developed iu 

 the very young specimens; but those forms which are found do not differ essentially from those of 

 the grown specimens, except in size. Until it is proved by facts that the pedicellariae of the young 



