ANATOMY, HISTOLOGY, MORPHOLOGY, AND PHYLOGENY. Ech. 27 
the Dendrochirote stem. The three families of Elasipoda do not repre- 
sent categories of equal value with the Aspido- and Dendrochirotoi 
(p. 597), and the Elasipoda are to be regarded as a branch of the 
Aspidochirote stem (p. 598). Diagram of Holothurian phylogeny 
(p. 599). The ancestral Holothurian had 10 simple tentacles, with 
ampullae, springing from the radial canals like the feet, which also 
had ampullae. The calcareous ring had 10 pieces ; the circular mus- 
culature was uninterrupted, and there were no retractors. The stone- 
canal, lying in the dorsal mesentery, opened to the exterior. The 
genital coeca wore paired. There were auditory vesicles, respiratory trees, 
and a simply-arranged system of intestinal blood-vessels. The gut 
had the characteristic curves, and the calcareous plates were lattice-like, 
with hexagonal faces. From this ancestor arose on one side the Aspido- 
chirote stem, on the other the Dendrochirote , as the result of diverging 
modifications of the ancestor (p. 600). As the result of these con- 
siderations, the author proposes a new classification of IJolothurians [ vide 
Systematic, pp. 47 & 48 ; the classification proposed cannot be said to agree 
well with the author’s phylogenetic tree], separating the Synaptidce from all 
others, since their tentacle vessels arise directly from the water-vascular 
ring, while in other Iiolothurians they arise from the radial water-vessels. 
The distinction between pedate and apodous Holothurians is unnatural ; 
strictly speaking, none are apodous, since the tentacles are feet modified 
in connection with the mouth. The Synaptidce are very ancient, but are 
not on that account the most primitive. They are not degenerate, but 
highly modified forms. 
The author gives the following tree of Holothurian phylogeny : — 
Protholothuria. 
