jg ECHINOIDEA. II. 



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the fio-ures on the plates in the best way. The simplest way is obviously to put together all the figures 

 f the same species, but a comparison of the figures of the different species is not made easier in 

 that wav and the general appearance of the plates cannot then be taken into account. The latter fact, 

 to be sure, has no real scientific value, but I willingly confess that I like to have the figures arranged 

 with some regard to the appearance of the plates. It does not seem to me that the arrangement in my 

 plates is so quite hopeless for comparing the figures of the different species. All the figures of pedicel- 

 lariae of the Echinothurids are put together on three successive plates, the first of them including all 

 the fio-ures of triphvllous pedicellarias ; and the numbering of the figures is constantly in transverse series 

 from the left to the right, so that the figures are at least easily found out, in any case much more easily 

 than in some of Professor Agassiz' plates, e. g. in (Revision of Echini : PI. VI, XXIV— XXVI, XXXVIII 

 and Challenger Echinoidea: PI. XXXVIII— XLV, where the numbering and arrangement of the figures 

 seem without any plan whatever. Regarding the quality of my figures I am sorry to say that I am 

 far from satisfied with several of them, and I likewise must agree that it might have been better to 

 give the direct enlargement of the figures instead of the number of the oculars and objectives. But, 

 on the other hand, the size of the pedieellariae has upon the whole no such systematic importance that 

 exact measurements are necessary, since generally they vary very much in size. 



In dwelling upon the many points of relationship between Phormosoma and Astheuosoma . 

 says Professor Agassiz (p. 82), I drew attention to the difficulties of describing the species of these 

 genera owing to the changes due to growth. On the strength of this remark Dr. Mortensen assumes 

 that I have stated that the two genera cannot be distinguished, and proceeds to ignore all that has 

 been said of the different species of Echinothuriae relating to the actinal and abactinal systems and 

 the spines, because he thinks the Echinothurids are not adapted for examination in the dry state. But 

 he claims to give a perfect classification based, first, upon the characters of the spines, as if his pre- 

 decessors had not mentioned them in any way; next upon pedicellarise, tube feet, pores and spicules, 

 the last of which he has previously informed us were of no systematic value! Having stated that the 

 genera Phormosoma and Asthenosoma cannot be distinguished, he then establishes a number of new 

 genera based wholly upon the structure of the triphyllous and tridentate pedicellarise. The latter show 

 a great variety of forms, and are of great systematic importance ; while the former have little system- 

 atic importance in Echinidae, they are considered by Dr. Mortensen of value for the determination of 

 the Echinothuriae. 



That the genera Phormosoma and Asthenosoma as understood by Agassiz cannot really be 

 distinguished, it seems to me superfluous to again demonstrate; Agassiz has not given any further 

 distinctive characters of the two <genera^, and both de Meijere and Doderlein agree with me in 

 the limitation given thereof in Part I of this work. As for the changes clue to growth , I might re- 

 mark that such changes are evidently upon the whole much smaller than Professor Agassiz thinks, 

 since in several cases these changes are due to the specimens belonging to different species or even 

 different genera. (See e. g. Phormosoma uranus and Pctcrsii Part I. p. 58 — 59.) For the purpose of 

 showing such changes, it seems to me highly important that the identification of the differently sized 

 specimens be made as certain as possible by using all characters available for specific identification; a 

 record of the changes undergone by a species during growth is worth less than nothing w T hen the speci- 

 mens upon which the changes are described do not belong to the same species or even the same genus. 



