■1. Ech. 
ECHIWODEUJ^IATA. 
orifice only. In Trichaster (10 a), the existence of a single water-pore in 
each interbrachial space was adduced ; in the distal portion of the arms 
of this species and of Asterophyton asperum each pair of ambulacral 
papillae is transformed into a sort of pedicellaria, whose two mobile 
hooks are however, though divergent, not opposed against each other. 
Of Ludwig’s third paper (10 c), the first portion is devoted to a detailed 
description of the skeletal parts of the arms and mouth in OphiuridcQ, to 
the reduction of the oral parts to the brachial ambulacral, ad-ambulacral, 
and sub-ambulacral plates and ossicles, and to the homologies between those 
of the Starfish and the Brittlestar. The most essential points in Ludwig’s 
theory are the interpretation of the “ mouth-shield ” in OpJduridce as first 
inter-ambulacral, the “lateral mouth-shields” as second ad-ambulacrals, the 
“ mouth-frames ” as first ad-ambulacrals and second ambulacrals (suturally 
connected), and the “ peristomial plates” of Muller as first ambulacrals. 
While the first two pairs of tentacles derive their vessels separately from 
the radial ambulacral vessel in Asteridce, they are in Ophiuridoe derived 
from the annular peristomial vessel through a common bifurcating branch. 
[Ludwig’s theory leaves unexplained that his “first ambulacral ossicle ’ has 
none of the oral tentacles, and his “ second ambulacral ” two in the place 
of onej and therefore can hardly be accepted as completely satisfactory]. 
The second portion of this paper illustrates the important observation that 
the so-termed genital slits of the OpMuridce do not lead into the body- 
cavity, but into separate closed pouches in which the young of the vivi- 
parous Ophiuridcn are nursed, and into which the genital organs open 
through minute orifices. These pouches, which probably also are subser- 
vient to respiratory functions, are further homologous with certain organa 
(the “hydrospirae ”) in the Blastoidea. 
H^ckel (7) resords his observations on the “ cometoid ’’spontaneous 
division and regeneration in species of Ophidiaster {Lincicia), viz., the cast- 
ing off of the arms and the reproduction of 4-5 new arms, disc, mouth, 
madreporites, &c., from the basis of the rejected arms ; with the Recorder 
(1872) and others, ho regards the phenomenon in the light of “ alternation 
of generation ” (metagenesis). It is also regarded as giving great strength to 
the idea of the composite nature of the Echinoderms or “ A strocormus,’' 
in opposition to the solitary nature of the “ Astrotithene,*^ viz., the “ larva,” 
or “ Ecliinopcedium’' as it is termed by others. In relation to the more 
or less advanced “ centralization,” the Echinoderms are — 1, Prote- 
strellce (Asterice) ; 2, Antheatrellcn (2, Ophiurcej 3, Crinoida) ; or 3, 
Thec68trellce (4, Blastoida, 5 Echinidee^ 6, Holothuricd). The oldest, most 
primitive type, from which the others are derived, are the Starfishes 
(Protestrellce). As a type perhaps closely allied to the hypothetic “ Arch- 
estrella*' the Lower Silurian ITelminthaster ruthveni is cited, while the 
Siluvisiii Phractelmintha ’’ {CrossopodiUj Phyllodocites) are cited as the 
probable not coalesced ancestors of the oldest Starfishes, having the 
greatest likeness to isolated skeletons of A strolenoi^^ (viz., arms of star- 
fishes, &c.). 
Haeckel’s “ ’’-theory is criticised in the final remarks of 
Carpenter’s critical review (2) of the more recent attempts of various 
authors to hopiologize the parts of the basal (apical, ab-actinal) system of 
