UCUINOIUKA. II. 



specimens differ esseiilialK ' in stincture Ironi lliose of the j^rown ones ni\ positive statement, founded 

 on direct observations, that tlie\ are essentially alike ninst be accepted; b\- words alone it is not 

 refnted, e\en if it be tlie words of an authority so famous as Professor Agassiz. 



What most astonishes me in Professor Agassiz' objections a<)aiust the systematic use of the 

 pedicellaria.' is his disbelief in my account of the development of the pedicellarice. The whole matter 

 seemed me so clear and its correctness beyond doubi that 1 did not find it necessar\- to figure tlie 

 different developmental stages of all the different pedicellari;e in all the species. I might have filled 

 several plates with figures of developmental stages of pedicellarite. I have stated already in Part I. 

 p. 6 that I have found such stages of development in most of the species I have examined , and 

 this holds good also for those Echinoid.s, which I ha\e studied since then. When Professor Agassiz 

 states that the only addition made by me to the knowledge of the development of pedicellaria; is the 

 development of a triphyllous pedicellaria oi IVioriiiosoiiKt placnitn^ he has probabh' overlooked thi.s 

 remark as well as m\- figures of the de\-elopmental stages of a tridentate pedicellaria of Plinruiosown 

 placriifit. Indeed, in spite of Professor Agassiz' doubt of the correctness of m\- view of the mode of 

 development of the pedicellariie, I do not find it necessary to give more figures thereof. 1 think uo- 

 bod\' will follow the famous author in the belief that small pedicellarise are gradualh, through most 

 intricate processes, transformed into large ones, a belief which is sustained by no facts, against my 

 demonstration that the pedicellaria; develoj) at once to their final size. The reabsorption and rearrange- 

 ment constanth- taking place in the test can in no wa\- be compared with the rearrangements that 

 would be uecessar\' for transforming a small, fully formed pedicellaria to a larger one. The changes 

 in the test can all easih- be understood as caused h\ the processes of absorption in some places and 

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

 formed, e\'en more or less decorated edges, could never get the form of a valve of a large tridentate 

 pedicellaria. Even to suppose a process of intussusception would not help, the calcareous \alves not 

 being of a plastic matter like a plant-cell, but much more like some kind of crystalline structure. 



Regarding the relation of pedicellarite to the fossil forms Professor Agassiz remarks (p. 107): 

 Dr. Mortensen does not fail to percei\'e that pedicellarias 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 pa.s.sing, of the Irregular Echinoids . On this theme I have said (p. 8), after mentioning the descrip- 

 tion of the pedicellaria; of Prlancchiiius cornllinns b\' Cirooui and suggesting the possibility of also 

 finding pedicellarite in well preserved specimens of other fossil Echinoids: Of course, however, it will 

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

 structures also often give excellent characters, but they are far from being always reliable. The lormer 

 great incertaiut\ in the determination of the recent forms of regr.lar Echinoids (and I think it is not 

 nuich better with regard to the irregidar ones) may be taken to imply that there cannot be an\ great 

 certaint\- in the classification of the fossil forms either . — It seems to me that these few remarks are 

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

 other hand, the fact that in all the families treated in Part I the pedicellaria' are of so great 



■ 111 Eckinus the globiferous pedicellariie appear to have the blade generally .somewhat more open in young speci- 

 mens than in the grown ones, as is pointed out by Doderlein. (Op. cit. p. 211.) 



