2 IN 



II. Morphology; Phylogeny; Biology. 



The general homology ol Ihf loin iii;iiii lypes of the Echinoderni larvae 

 was so clearly poiiilod out by .loli. Miillcr in his classical memoir "('ber 

 den allgemeinen Plan in der h>ntsvickhing der luhinodermcn"') thai very 

 lit lie has had to be corrected-) or addetl, the main Ihing being that the 

 separate I'ronlal band of the Asteroid-larvae does not rei)resenl an essential 

 dilTerence from llu' oilier larvie, as.Ioh. Miiller thoughl il lo do. In the 

 light of liir more extensive knowledge ol' the larval forms now ac(|nired 

 il may be worth while lo pay some allenlioii to the special development 

 within each of the fonr lypes, to see how they develo|) From the |)rimitiv(' 

 generalized shajje into more or less highly specialized forms or, on the other 

 hand, are rednced into forms so simple that they are hardly recognizable 

 as forms derixcd Irom the true pelagic larval ty|)e. 



The Au rieu laria is tlie ty|)e in which the least amonnt oi specialization 

 a])]K'ars lo have taken place, due allowance being made for the fact that 

 we know comparatively less about tlu' I lololhurioid larva' than of the 

 three other main groups. The simplest form is that found within the genus 

 Ilololliuria ( — unless it should turn out lo be much more speciahzed in 

 the more advanced stages of development, which does, however, not seem 

 very likely ). The vibralile band hardly shows an indication of the typic- 

 al larval processes, the larva in fad looking almost like a diagram of the 

 primitive Echinoderm-larva, as regards its outer shape ( as to its inner 

 structure il is less simple — ). Only simple calcareous bodies are known 

 lo occur, irregular stars or spherical bodies'*), no wheels. The larva* of 

 Sijiutpld and Sticliopus are only a little more specialized, the vibralile band 

 forming small processes corresponding to those of the other Kchinoderm- 

 larva>. In the Sijnnpla-hM'va calcareous bodies are formed in the shape 

 of eleganl wheels. 



Till' Am iciildiid pamdoxa being in all probability only a decalcified 

 luhiiiopliilciis li(ii}sversiis, only one group of Holothurian larva is known, 

 which represeiUs a more specialized form of the Auricularian type, viz. 

 the larva Auiirularia minor, plicala and uudibmiuhiala. While .1. minor 

 is still comj)aralively easily referred to the |)rimitive type, A. plicata is 

 considerably more specialized, but the climax is reached by .1. niidihrdii- 

 cliiala in which the vibralile band develo|)s to such an extraordinary degree 

 of complication that il is difficult enough lo recognize the original type. 

 Auricidarid (inlarclica, though somewhat specialized in other directions, 



') Abhandl. d. Akad. Berlin. 16.33. Taf. 11. 



-) Conip. the author's Memoir "Die Eehinodermeniarveii d. Plankton-Hlxpedition" p. 8. 

 ') The Aiiriciilaria spharrif/era (.loli. Miillers's " 'Auriciilaria mil Kiiijeln") may well 

 be suggested lo lieloiig lo tlie genus llololhiiria. 



