79 



although certainly other views have partially prevailed. That some Holothurise (Synapta) in 

 their exterior habitus, have a striking resemblance to worms, is a well-known fact, and has 

 given rise to the popular denomination „worm-cucumbers". We have likewise a peculiar 

 class among the \ermes, the so-called trunk-worms (Gephvrea), the organisation of which 

 exhibits several remarkable points of resemblance with the Holothurians, and therefore 

 also has formerly been referred to the type of the Echinodenns. Since however, as above 

 stated, we have in the Holothurise really the most divergently developed group of Echino- 

 derms, it cannot actually be here that we should seek for the original ancestry of the Echi- 

 noderms ; although it can not be denied that we may also here observe a remarkable retro- 

 gression to the same type which may be assumed as basis for the oldest and most original 

 Echinodenns, the star-fishes. 



In opposition to the theory above stated as to the phylogenetic relationship of the 

 Echinodenns to the Articulata, the ambulacral or water-system has been adduced as presum- 

 ably exclusively peculiar to the Echinodenns. It can certainly not be denied that this organic 

 system affords, by its extremely peculiar and complicated development and functions, one of 

 the most distinctive characteristics of the Echinoderms; but it is by no means on that 

 account decided that nothing of the kind is to be found in other animal types. We have 

 frequent instances of one and the same organic system developing itself in different groups 

 of animals in a very different manner, and exercising quite dissimilar functions; so that the 

 originally common fundamental form may be difficult to recognise. We have in the Vermes 

 a very extensive organic system in the form of tortuous canals, opening partly externally 

 partly in the cavity of the body, and appearing decidedly in certain cases to be water-ducts; 

 while in other cases they have secretory functions. Where the body is evidently devided 

 into segments, these vessels appear to be arranged symmetrically in each segment, and 

 have therefore in the annelides been indifferently denominated segmental organs. It may 

 be assumed that we have here the analbgon of the ambulacral system in the Echinoderms; 

 at least it appears to me that there cannot be adduced any decided proof to the contrary. 

 There is another characteristic which seems to be foreign to the Vermes, and which is so 

 prominent in the Echinoderms that even the whole type has derived its name therefrom, 

 namely the cuticular skeleton more or less strongly developed by calcareous secretions, to 

 which we may add that in the Asterides and Crinoides there is even another sort of interior 

 skeleton which exhibits a so striking habitual ressemblance to the vertebral column in the 

 Vertebrata that the single segments even bear the same name (vertebra'). In examining 

 the real Vermes we certainly do not find anything analogous; but this characteristic is by 

 no means foreign to the whole tribe of Articulata. In the Crustaceans we have frequent 

 instances of the integuments, by absorbing lime, assuming quite as firm a consistency as in 

 the Echinoderms; and by interior processes of this cuticular armor, there is also formed 

 here (Decapods) a sort of interior skeleton, which serves partly for the insertion of the 

 limbs with their muscles, and partly also as support for interior organic systems (the ner- 



