ECHINOIDEA. II. j. 



speciniens differ essentially ' in structure from those of the grown ones my positive statement, foiinded 

 on direct observations, that the\- are essentialh alike mnst be accepted; b\' words alone it is not 

 refnted, even if it be the words of an anthority so fanious as Professor Ag as s i z. 



What most astonishes mo in Professor Agassiz' objections against the systematic nse of the 

 pedicellariæ is his disbehef in my account of tlie development of the pedicellariæ. The whole matter 

 seemed me so clear and its correctness beyond doubt tliat I ihd not find it necessar\- to figure the 

 different dexelopmental stages of all the different pedicellariæ in all the species. I might have filled 

 several piates with fignres of developmental stages of pedicellariæ. I have stated already in Part I. 

 p. 6 that I ha\e fonnd snch stages of development in nKjst of the species I have examined, and 

 this holds good also for those Echinoids, which I have studied .since then. When Professor Agassiz 

 States that the only addition made by me to the knowledge of the development of pedicellariæ is the 

 development of a triph>llons pedicellaria of Phortiiosoma placciUa^ he has probablv overlooked this 

 remark as well as m\- fignres of the developmental stages of a tridentate pedicellaria of Phormosoma 

 placciitii. Indeed, in spite of Professor Agassiz' donbt of the correctness of \\\\ view of the mode of 

 develojjment of the pedicellariæ, I do not find it necessary to give more fignres thereof. I think no- 

 body will follow the famous anthor in the belief that small pedicellariæ are gradnalh', tlnongh most 

 intricate processes, transformed into large ones, a belief which is snstained b\ no facts, against m\' 

 demonstration that the pedicellariæ develop at once to their final size. The reabsorption and rearrange- 

 ment constantl\- taknig place in the test can in no way be compared with the rearrangements that 

 wonld be necessar\- for transforming a small, fnlly formed pedicellaria to a larger one. The changes 

 in the test can ail easily be understood as cansed by the processes of absorption in some piaces and 

 apposition in others, but b\ mere apposition a \alve of a small tridentate pedicellaria with fnlly 

 formed, even more or less decorated edges, conld never get the form of a val ve of a large tridentate 

 pedicellaria. P)ven to snppose a process of intnssnsception wonld not help, the calcareons valves not 

 being of a pla.stic matter like a plant-cell, but luuch more like some kind of cry.stalline structure. 



Regarding the relation of pedicellariæ to the fossil forms I-'rofessor Agassiz remarks (p. 107): 

 Dr. ^klortensen does not fail to perceive that pedicellariæ are not likely to be of frequent use in the 

 determination of fossil form.s, and for that reason condemns the classification of all fossil forms, and, 

 in passing, of the Irregular E^chinoids . On this theme I have said |p. 8), after mentioning the descrip- 

 tion of the pedicellariæ- of Pelanccliiiins coy(dli)iiix by (irooni and suggesting the possibilit\- of also 

 finding pedicellariæ in well preserved speciniens of other fo.s.sil P'chinoids: Of conrse, however, it will 

 always be a rare thing — generalh we have liere to be content with the tests (and the spines). These 

 strnctures also often give excellent characters, but they are far from being alwa\-s reliable. The former 

 great incertainty in the determination of the recent forms of regular Px^hinoids (and I think it is not 

 much better with regard to the irregnlar ones) ma}' be taken to imph- that there cannot be an\- great 

 certaintx- in the classification of the fossil forms either . — It seems to lue that these few remarks are 

 indeed very moderate and can not be said to :condemn the classification of all fossil forms ; on the 

 other hånd, the faet that in all the families treated in Part I the pedicellariæ are of so great 



' In Bckinus the globiferoiis peilicellariæ appear to have the blade geiierallv .soiiuwhat more o)ieii in vomig speci- 

 niens thaii in the grown ones, as is pointed out hv Doderlein. (Op. cit. p. 211.) 



