I. Morphological and Physiological Works of a General Character. 5 



oral lobe (when present] and may be called anterior. The condition of Bipinnaria 

 also shows that the left anterior enterocoel becomes the schlauchfdrmiger Canal 

 or axial sinus of the adult. 



Semon ( l ) lays much stress on one point of fundamental difference between the 

 Holothurians and the other Echinoderms. Two tentacular systems in different 

 radii, and not one only, are developed from the beginning as outgrowths of the 

 water-vascular ring ; and this difference is better explained by supposing all 

 Echinoderms to be derived from a common ancestral form [Pentactaa] , than by 

 regarding Holothurians as degenerate Urchins which have developed a second 

 tentacular system. At the same time the author reasserts his belief that the 

 primary tentacles of Holothurians are specially homologous with those of other 

 Echinoderms, and that their radial water- vessels are structures peculiar to themsel- 

 ves [see Bericht for 1888 Ech. p 3] . He thinks it possible that the radiate muscular 

 system of Echinothuridae may have been derived from such structures as the 

 longitudinal muscles of Holothurians, as supposed by the Sarasins [see Bericht for 

 1888 Ech. p 22]; but both, together with the integumental muscular system of 

 all Echinoderms, are more probably derived from the indifferent condition of a 

 continuous longitudinal musculature, on which the Holothurians present very little 

 advance. The Cystideans are distinguished by the absence of a water-pore, so 

 characteristic of other Echinoderms, while a body-musculature seems to be also 

 wanting. Agclacrinus is not a transition from Cystidean to Starfish, as supposed 

 by Neumayr [see Bericht for 1888 Ech. p 5] ; for the so-called ambulacral pores 

 are not likely to have been related to ampullae in a fixed form, like those of a 

 Starfish are, while water-pore and musculature are absent, though the Starfish 

 ancestors must have possessed them. The same applies to Mesites, the supposed 

 transition form between Cystids and Urchins, while its interambulacral plates are 

 fixed, not overlapping as in Palseechinidae, and the pores for the tube-feet pass 

 between, not through, the ambulacral plates. The marginal position of the anus 

 in Echinocystites (W. Thorns.) is not a Cystidean character, while the anal pyra- 

 mid also occurs in Holothurians, and is an analogous structure to the oral plates 

 of Crinoids. Since the Cystideans have no madreporite, the position of this organ 

 in Echinocystites is in no way indicative of a relationship to Cystideans, as stated 

 by Neumayr. The genus probably represents a very primitive Echinid type, in 

 a phylogenetic stage at which both anus and madreporite are still excentric. No 

 equivalent of the oral calcareous ring of Holothurians occurs in Echinids, the 

 auricles of this group being primitively but muscular apophyses with only acci- 

 dental relations to the radial nerves and water-vessels. But ontogeny shows that 

 the oral ring of Holothurians is intimately associated with the water-vascular 

 system, serving as a support to the tentacular apparatus. The insertions and 

 origins of its muscles are in the same radii ; while the retractors of the lantern in 

 Echinids and Echinothurids have radial origins but iuterradial insertions. - The 

 similarity between the calyx of a Crinoid and the apex of an Urchin is probably 

 due to a mere convergence which is developed in relatively young forms, and not 

 to a true homology. The plates of the oral and apical systems have no direct 

 relations to the enterocoel, and their relative positions are due to the fact that 

 the longitudinal axis of all Echinoderms is altered, during the change from the 

 Dipleurula- to the Pentactula-stage, in such a way that the right side of the 

 larva becomes dorsal and the left ventral. The various classes of Echinoderms 

 early diverged from an ancestral group with certain common characters and others 

 which were still in an indifferent condition and have developed in different ways 

 in the different groups. 



Kowalevsky has injected carmine into the water-vessels of Starfishes and finds 



