232 



supporting apparatus for the muscular system. (Comp. e. g. fig. 34, p. 88). It 

 is of cousidiMahk' intcrcsl lo Irai-c this unusual (k'velopincnt ol' a (piitr 

 indilR'ronl flenuMil into a slruclure of liie grt-alesl perfi'cUon. 



KiMlucfd larval forms, so common in the oilier classes of the lichino- 

 (leruis. are only rarely met with in lu'hinoicls. in fact were hilheilo (piitc 

 unknown. 1 have had the good fortune of discovering two most interesting 

 cases of reduction - not counting the I'^chinopluleus lidiisversiis — , in 

 which all the arms, excepting the posloral ones, have disappeared. One 

 of them, the larva of Pcroiwlla Lesueiiri, is still recognizable as an I'Lchino- 

 pluteus, the posloral (and sometimes also the posterodorsal) arms still 

 remaining, and a larval skeleton, rudimentary but still distinct 1\ leferable 

 to the normal skeletal typi'. being developed. The vibratile baud has dis- 

 appeared, the lar\a being covered only by a uniform cilialion; only in 

 some exceptional cases a rudimenlaiy band is developed (|). IKi: fig. 18). 



In the other vixsc, Ilcliucidaris criilhio(/i<imnui, the reduction has gone so 

 far that there is not the slightest trace of the Fluteus-shape left. This 

 larva recalls tiie barrel-shaped larva> of Comatulids and Dendrochirotes, 

 but dilTeis markedly from them in having only one. not very distinctly 

 dilTerenlialed ciliated ring. 



The existence in Kchinoid-larva* of a pupa-stage corresponding to that 

 occurring in I lololhurians and Ophiurans has been emphasized by t^as- 

 well (irave, who has observed transverse ciliated rings on the newly 

 metaniori)hosed sea-urchin of Mellita lesludinaUt. (Oj). cil. Fig. 10. j). 178). 

 I have not made any corresponding observations and shall therefore refrain 

 from commenting on the possible existence in Echinoids in general of such 

 a pupa-stage. Whether the HcUovidaiis ciiilhnxjrammaAiwxa is to be 

 regarded as an indication in that direction 1 shall leave undecided. 



The few Crinoid-larva^ known being all of the vermiform type there 

 is no reason to mention them in the ])resent connection. With the greatest 

 expectations we may look forwards lo the future discovery of some typical 

 pelagic Crinoid-larva: the study of its relations to the other four main 

 types of Kchinoderm-larva? will be of extreme interest. The existence of 

 such a pelagic Pelmatozoan-larva would seem almost beyond doubt, 

 though possibly not in any of the recent Crinoids. Hut these latter repre- 

 sent — in spite of the enormous development of the Comatulid-type — 

 only a diminutive fraction of the whole group of the Pelmatozoa. It would 

 hardly seem too bold to fancy that at least some of the fossil Pelmato- 

 zoans, especially of the numerous Cyslideaus, had truly pelagic larva-. It 

 is very sad that we have no hope of learning anything about them, it 

 being in the highest degree unlikely that such larva* should have been 

 preserved in a fossil state. Fritsch, it is true, has described an organism 



