The author of the present work has for a long time realized that the 

 study of the larvae would have an important bearing also on the classi- 

 fication of the adult forms, and it was, indeed, mainly from this point 

 of view that the investigations recorded in this work were undertaken. 



While it is obvious enough that the pelagic larvge must be of consider- 

 able importance for the geographical distribution, the question whether 

 they have also a bearing on classification is, however, not so easily settled. 

 It is, of course, undeniable that their organization and shape is stamped 

 by the adaptation to the pelagic life; but are the larval characters purely 

 secondary adaptations, which cannot possibly afford any clue to the 

 natural affinities of the adult forms? The author has gradually become 

 more and more convinced that this is not the case, but that they do really 

 have a classificatory value. Already in the Part I of the "Ingolf" Echi- 

 noidea (1903. p. 141) the possibility of finding in the larval forms facts 

 that might be of value for classification was hinted at, the great dif- 

 ference known to exist e. g. between the larva of Sphaerechinus granulans 

 and those of the Echinus-species being mentioned as indicating "at all 

 events, that very interesting things may be found here." 



The facts hitherto made known regarding the larval forms of Echino- 

 derms would seem upon the whole to support the idea that there is a 

 distinct interrelation between the larvae and the adults, that the classi- 

 fication of the larvae corresponds to that of their adult parental forms. 

 Thus e. g. the Spatangoid larvae have the pecuUar character in common 

 that there is a long unpaired process from the hindpart of their body, 

 and not a single exception is known to this rule. The larvae of Echinus, 

 Psammechinus and Paracentrotus all agree in having in their first stage the 

 body considerably elongated beyond the stomach and supported by 

 an elongated, clubshaped body rod, while in the later stage this rod 

 becomes absorbed, so that the body is shortened, being in the same time 

 provided with vibratile epaulettes, while no posterior transverse rod is 

 developed. It would thus seem that here we have a distinct larval type 

 pecufiar to the family Echinidae. The Clypeastroid larv« hitherto described 

 {Echinocyamus pusillus, Echinarachnius parma and Mellita testudinata) 

 all agree in the general character of the larval shape and the structure of 

 the larval skeleton (the body skeleton forming a basket structure), so that 

 it has the appearance that there is a Clypeastroid larval type as' distinct 

 as the Spatangoid type. Among the Asteroids it seems evident that there 

 is a distinct larval type, the so-called Brachiolaria, pecuUar to the family 

 Asteridae, characterized mainly by its round Brachiolarian processes 

 while the type of Bipinnaria asterigera (the first Echinoderm larva describ- 

 ed) appears to be characteristic of the family Luidiidae. 



