22 Ech, 
ECHINODERMATA. 
in all Echinoderms ; (2) cavities of enteroccelic origin, well-defined in 
Echinoids , Ophiuroids, and Asteroids ; (3) the lacunar system well- 
developed in Synaptids , Holothurians , Echinoids, and Crinoids ; rudiment- 
ary in Asteroids and Ophiuroids. It comprises an absorbing apparatus, 
collecting the products of digestion, and branches distributing them to 
the gonads, to certain glands, and to the radii. Synaptids (pp. 574 & 575). 
Holothurians (pp. 576-583). In Cucumaria planci the extremity of the 
dorsal marginal lacuna is transformed into a lymphatic gland. In Holo- 
thuria impatiens the whole oral lacunar ring is similarly transformed. 
The genital organs in Holothuria impatiens arise from a mass of cells 
(pi. xxx, fig. 76) which appear to be placed in the dorsal marginal lacuna 
of the intestine. Crinoids (p. 584) : the oral lacunar ring is transformed 
into a lymphatic gland, for which the name “ organe spongieux ” is pro- 
posed. Enterocoelic cavities ( Echinoids , Asteroids , and Ophiuroids) pp. 585- 
590. In these three groups, the enterocoelic vesicle, primitively * inter- 
posed between the water-tube and the dorsal pore, stretches itself along 
the whole length of the water-tube, and becomes the axial sinus. The 
water-tube approaches the pore, but always retains a communication with 
the enterocoele. The ovoid gland appears as a differentiation in the axial 
sinus, arising in Amphiura squamata and Asterias tenuispina as a thickening 
of its inner wall. Development of Gonads in Echinoids , Asteroids , and 
Ophiuroids (pp. 590-598). In Echinoids the genital rachis grows from a 
thickening in the wall of the axial sinus. In Asteroids and Ophiuroids the 
genital rachis grows out from the ovoid gland. Schizoccelic cavities of 
Echinoids , Asteroids , and Ophiuroids (pp. 598-601). Lacuno-plastidogenous 
System (pp. 601-616). Echinoids (pp. 602-605). Ophiuroids (pp. 605- 
608) f Asteroids (pp. 608-610). The lacunar systems of different classes 
are probably not homologous, their resemblances being due to con- 
vergence. The ovoid gland is perfectly homologous in Echinoids , 
Asteroids , and Ophiuroids , but the dorsal organ of Crinoids is probably not 
homologous with the ovoid gland, since it does not develop in connection 
with the enterocoele vesicle, and has not the lymphatic structure of the 
ovoid gland. In Holothurians there is also no homologue of the ovoid 
gland, since the enterocoelic vesicle becomes obliterated. The sexual 
cells originate in all cases from the coelomic epithelium. Genital organs 
(pp. 616-629). Development of the ova (pp. 616-619). Development of 
the spermatozoa (pp. 619 & 620). Genital orifices (pp. 620-623). 
Hermaphroditism (pp. 623-629). Morphological value of Arms and 
Eadii (pp. 631-635). Phylogeny (pp. 643-652). The author supposes a 
number of ancestral forms, for which the following names are proposed : 
(1) Prosynapta , ancestor of Synaptids (p. 643) ; (2) Proholothuria , 
ancestor of Holothurians (pp. 643 & 644 ) ; (3) Procystus , ancestor of 
Pelmatozoa (p, 644); (4 ) Proechinus, ancestor of Echinoids (pp. 644 & 645); 
(5) Proaster , ancestor of Asteroids and Ophiuroids, These ancestral forms 
are directly descended one from another in the above order, and at the 
same time each gives off lateral branches, which become the Synaptids , 
Holothurians , &c., the main stem being directly continued by the Asteroids. 
