3'64 Dr. O. Hamann on the PhyJogeny 



stroke, that anatomically and histologically it is impossible 

 to accept the Crinoiclea as the stock-group of the Ecliino- 

 dermata. Our present standpoint can only be that on the one 

 side stand the Crinoidea and on the other the Asterida, from 

 which the Echinida may be derived without any difficulty, 

 and lastly the Holothurige. While the last-mentioned three 

 groups can be derived, in their organization, from one 

 another, the Crinoidea stand without any connexion. 



Quite peculiar and present in no [other] group are the 

 remarkable calycine pores, through which the body-cavity 

 communicates with the outer world. Above all, however, 

 the nervous system is not in the primitive form which occurs 

 in the Asterida. This (the nervous ring and ambulacral 

 nerve-stems radiating from it) is no longer situated epithelially, 

 but subepithelially (Ludwig). The most important part of 

 the nervous system of the Crinoidea is, however, placed 

 dorsally, in the centro-dorsal plate ; from a central organ 

 fibrous cords are given off into eacli arm, and from these 

 similar cords to the muscular fasciculi and appendages of the 

 arms, as already described by W. B. Carpenter in 1865. A 

 dorsal nervous system so constructed does not occur in the 

 Asterida (Ophiuri), Echinida, or Holothurige. 



We have also to consider above all the body-cavity of the 

 Crinoidea, which is probably to be regarded as a schizo- 

 coelar cavity, and the sexual organs, the structure of which 

 differs from that of those of the other groups. 



I think, therefore, that the Crinoidea may be most natu- 

 rally regarded as a lateral branch of tlie Echinodermata, 

 about the origin of which we are still in doubt. As coming 

 nearest to the truth we may perhaps suppose that the Cri- 

 noidea and the Asterida have sprung from a common root. I 

 regard the latter as the stock-form of the most nearly allied 

 Echinodermata, referring especially to the structure and ecto- 

 dermal position of the nervous system. How I suppose the 

 Echinida to have originated from them will be shown in the 

 following pages. 



Consequently I come to the conclusion that those naturalists, 

 with Hiickel, G. 0. Sars, and Lange at their head, who 

 place the Asterida at the head of the Echinodermata, have 

 hit upon the right course. Palasontology, it may be repeated, 

 supports neither the one interpretation, according to which, 

 the Crinoidea are to be regarded as the most ancient class of 

 the Echinodermata, most nearly approaching the stock-group 

 (Claus), nor the other view, just maintained by me, as the 

 tAvo groups make their appearance together at the same time 



