626 SUMMAKY OF CUREENT RESEARCHES RELATING TO 



Tlie water-vascular system has a similar character in all groups, but 

 the Crinoids have no madreporite, and their pore-canals do not open 

 directly into the stone-caual, but into superficially placed cavities of the 

 enterocoel. The valvular arrangements of this system are of great 

 interest, but they are wanting in Ophiuroids and Crinoids, where they 

 are replaced by transversely disposed muscular fibres which traverse 

 the lumen of the vessels. 



All the groups are provided with genital tubes ; in Crinoids they 

 are placed in the arms, in Ophiuroids in the dorsal wall and in the 

 walls of the bursae, and in Asteroids and Echinoids in the dorsal wall 

 of the disc. The several groups present differences in the place of 

 maturation of the primordial germ-cells, for in Crinoids they ripen in 

 the pinnules, and in Ophiurids on the walls of the bursse. 



In addition to smooth and transversely striated muscular fibres, there 

 are in Ophiuroids peculiar obliquely striated fibres. Epithelio-muscular 

 cells have been found in Holothurians, Asteroids, and Crinoids. The 

 musculature is partly of epithelial and partly of mesenchymatous origin. 

 The Crinoids are remarkable for spindle-shaped muscular fibres, which 

 are found in the arms as well as in the pinnules and cirri. 



The glandular organ or so-called heart is not the central organ 

 of the blood-lacuna-system ; muscular fibres are never found in its 

 walls. It is impossible to say at present what the function of this 

 organ is ; the only thing which can be said with certainty is that 

 the organ has a glandular structure. The connection between it and 

 the genital tubes, which is to be seen in Asteroids and Crinoids, is of 

 significance. 



With regard to the structures of the schizocool, it is to be noted that 

 there is a, very well developed cavitary system in Asteroids which has 

 the form of clefts and spaces in the connective substance ; in the 

 Ophiuroids they are less extensive, and in the Crinoids they are repre- 

 sented by the longitudinal canals which lie beneath the ambulacral 

 nerves. 



The author's determination to deal with the phylogeny of the 

 Echinodermata has wavered as his work proceeded, for he has been led 

 to see of how subjective a nature such a representation is. Of one point 

 only is he firmly convinced, and that is, the Asterids are connected 

 with the Echinids, and that the latter may be derived from the former. 

 The Holothurians appear to be forms which have undergone degenera- 

 tion ; many characters speak to their derivation from Echinids ; the 

 Crinoids seem to be the most highly organized forms, and with the 

 Ophiuroids form a group which have no specially close relation to the 

 others, save that they are all derived from an ancestor in which a 

 water-vascular system, a coelom, an ectodermal nervous system and 

 definite calcareous plates were already developed. With regard to 

 Semen's recent attempt to map out the phylogeny of the group, 

 Dr. Hamann remarks that, in the present state of our knowledge of the 

 development of Echinoderms, it is too early to speak definitely of a 

 Pentactula-stage of a Pentactaea ; nor does he think it correct to say 

 that there is such a stage in all groups, for the structures which have 

 been spoken of as one and the same stage are different, and show 

 undoubted modifications. Further objections are raised to the views of 

 Semon, and it is, in conclusion, suggested that weight should still be 

 attached to the homologies of the calcareous plates. 



