12 ECHINOIDEA. II. 



which nia\ tlirow aiiy light on the subject . But the stndy of pedicellariæ lia.s onl\ added a new 

 factor differing in no way in its potentialit\- from those formerly in nse , and there are several diffi- 

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

 they \ar\- with age. They form no exception and do not appear fnlly fledged in the embryos and 

 > oung speciniens, in spite of I)r. ]\Iortensen's statement to the contrary; thongh he ackuowledges that 

 there is in literatnre next to no more exact acconnts of the development of the pedicellariæ of Echi- 

 noids. Certainh- betore niaking sucli a sweeping iise of the minnte and often infinitesimal characters 

 supplied Ijy pedicellariæ for classification it wonld have been instrnctive to trace the development of 

 the several kinds of pedicellariæ, and obtain some data regarding the e.xtent and nature of the vari- 

 ation of pedicellariæ dnring their growth. The only addition made b\ Dr. INIortensen to our know- 

 ledge of the de\elopment of pedicellariæ is shown on Figs. 15, 24, 30 PI. XII of the Ingolf Echinoidea, 

 giving tliree stages of a triph\llons pedicellaria of Phormosoma placenta. As long as \ve know so little 

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

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

 place in the calcareous mass to make a small fulh' formed pedicellaria become a larger one . Ever\" 

 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 piates in the interambnlacral areas, and 

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

 be . — Further Professor Agassiz quotes niy remark (p. 9): When no pronounced difference is found 

 between large and small pedicellariæ, it nia\ in faet be impossible to decide whether a certain speci- 

 nien is to lie regarded as a large or .small form and adds that surely this acknowledgement that 

 the pedicellariæ cannot be classified ma\' throw some doubt on the statement that the pedicellariæ 

 give absoluteh- 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. 67-72). 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. Only a few remarks mav be added. 

 I waut to State explicitly that I quite agree with the remark that the new factor (the pedicellariæ) 

 differs in no wa\- in its potentiality from those formerly in use ; it can never be said beforehand with 

 certaint) whether the pedicellai4æ — or any other factor — are of primar\' importance in some group 

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

 racters. I ha\e never stated that the classification has always to be based on the pedicellariæ 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 valne than the cha- 

 racters in the pedicellariæ. — The assertion that the pedicellariæ do not api^ear fully fledged in the 

 embryos and >onng specimens in spite of Dr. M.'s statement to the contrary* is quite unjustified. M\- 

 statement is not founded on the accounts thereof in literature but on niy 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 pedicellariæ ma\- not perhaps be developed in 

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

 the grown specimens, except in size. Until it is proved b>- facts that the pedicellariæ- of the young 



