20 Ech. 
ECHINODERMATA. 
spaces, since they owe their origin to different processes. Lining and 
vibratile organs of the coelome (pp. 397-404). Synaptids (398-401). The 
ciliated funnels are probably completely homologous with the urns of 
Sipunculu8. In Synapta inhcerens euigmatic formations occur on certain 
parts of the wall of the coelome as little rounded papillae filled with 
connective tissue placed radially round a central nodule, and covered with 
flat epithelium (pi. xxiv, fig. 13). Holothurians (p. 402). Crinoids : 
ciliated cups (p. 402). In Echinoids (p. 403), the coelomic fluid is kept 
in motion by globular organisms, with a long flagellum, floating in the 
liquid, and resembling spermatozoa. Ophiuroids (pp. 403 & 404). 
Asteroids (p. 404). Blood fluids (pp. 404-406). Digestive tract (pp. 407- 
416). Holothurians and Synaptids (p. 407). Crinoids (pp. 407 & 408). 
Echinoids (pp. 408-410). Ophiuroids and Asteroids (pp. 410 & 411). The 
blastopore only becomes the anus in Holothurids and Synaptids. In all 
others the digestive tract ends blindly for a certain period, a condition 
persisting in Ophiuroids and some Asteroids. The secondary anus is per- 
forated independently in the different groups, as shown by the different 
positions occupied. Appendages of the digestive tract (pp. 410-413). 
Histology (p. 413). Organs of reserve (pp. 416-426). In Synaptids 
,(p. 417), probably represented by modified amibocytes (pi. xxiv, fig. 15) 
found in various organs. In Holothurians (p. 418) reserves evidently 
contained in the numerous muriform amibocytes abundant in all the tissues. 
Crinoids (pp. 419-425). The sacculi probably represent reserve material, 
by means of which the animal can repair evisceration. Their structure 
and development is described (pi. xxiv, figs. 17 & 18). The yellow cells 
so abundant in the skin are looked upon as wandering amibocytes, carry- 
ing reserve products. Echinoids (p. 425). Ophiuroids and Asteroids 
(p. 426). Nervous system (pp. 445-458) : it consists at its maximum of 
complication of three parts — (1) the epidermic nervous system, constant 
in all classes, innervatiug the skin, ambulacra, and digestive tract ; (2) 
the internal nervous system, well developed in Synaptids , Holothurians, 
Asteroids , and Ophiuroids , much reduced in Echinoids , and wanting in 
, Crinoids . It is probably of mesodermic origin, and innervates the 
motor muscles ; (3) the enterocoelic nervous system, wanting in Holo- 
thurians and Synaptids , enormously developed in Crinoids. It is 
certainly of enterocoelic origin, and innervates muscles. Evolution of 
epidermic nervous system (pp. 446-448). Ectodermic cells of the nerve 
centres (pp. 449-452). Nervous system of Asteroids (pp. 452-458) ; of 
. Ophiuroids (pp. 458-472) ; of Echinoids (pp. 472-479) ; of Crinoids 
■ (pp. 479-481) ; of Holothurians (pp. 482-484) ; of Synaptids (pp. 484- 
,486). Phylogeny of nervous system (pp. 486-488). The nervous system 
was primitively superficial in all groups, and has migrated inwards inde- 
pendently in different forms : in Echinoids by iuvagination, in Ophiuroids 
by a kind of epibole, and in Synaptids and Holothurians by delamination. 
The separation of the nervous system into an epidermic and an internal 
layer appears to be produced secondarily, since the nerves they emit do 
not correspond in the different groups. The enterocoelic nervous system 
