INTRODUCTION. 
Echin. 5 
the various theories, and elaborating the views already expressed in (19) 
Zool. Rec. 1900, and (18) Zool. Rec. 1901. The memoir (245) in which 
Russo sums up his researches, expresses somewhat different views. In 
Holothurians, he says, the sexual cells originate (a) in the wall of a 
mesentery formed by the coalescence of the horns of the left posterior 
coelom. The same is the case in Crinoids, but here this series a disappears 
at the end of the larval stage, while there are added two other series : ( b ) 
the genital stolon, which is axial, (c) a series of perioesophageal cords, 
which become connected with the series b and with the rachides of the 
arms, but not with series a. In Ophiuroids and Asteroids, series a pro¬ 
liferates into a genital ring, on which (d) the interradial genital glands 
develop. In Echinoids the same development is carried a stage further by 
atrophy of the ring between the glands. Thus Holothurians and Crinoids 
are primitive in the possession of the single series a, though this series, 
functional in Holothurians, disappears in Crinoids. Although he places 
these two classes together, with Holothurians as the more primitive, Russo 
is nevertheless inclined to admit their common descent from a Dipleurula , 
through £ the primitive Pelmatozoon ’ and the Cystids. His derivation of 
Blastoids from Crinoids seems based on a confusion of spiracles with 
hydrospires, and on a misconception of the morphology of those structures. 
As to the origin of the other section of the Echinoderms, he expresses no 
opinion, but regards the Asteroids as the most primitive, and the Echinoids 
as evolved from Ophiuroids. This hypothesis, one may retort, “ attende 
ulteriore conferma, specialmente dalla ” Paleontologia “ comparata ! ” 
MacBride’s big memoir on the development of Echinus esculentus 
comes into 1903, but in three preliminary notes (181-183) he brings out 
some important points, such as the presence of a rudimentary right 
hydrocoel, the transverse segmentation of the coelom, as first made known 
by Bury, the origin of the epineural and perihaemal spaces, the lantern, 
the ovoid gland which is a genital stolon ; in short, “ the main features of 
the development of Asterina can be recognised in Echinus ” though much 
modified. Theel’s account of the development of Echinus miliaris (277) 
differs in some points from MacBride’s results in E. esculentus. Thus, 
the amniotic pore closes in the latter but not in the former; the developing 
hydrocoel forms a horseshoe in E. miliaris , but is at first a flattened 
pentagon in E. esculentus , becoming a ring when pierced by the stomo- 
daeum ; the teeth, according to Theel, are formed in invaginations of ec¬ 
toderm, but, according to MacBride, in outgrowths of the left posterior 
coelom. The observations of Grave (105) on Mellita seem to support 
MacBride as regards the masticatory apparatus ; but it is possible that 
Theel has observed appearances which have merely escaped the notice of 
the other workers. 
HfiROUARD (126) bases an “anatomie comparee des Echinodermes ” on 
the homologies between the body-wall of Holothurians and that of the 
other Eleutherozoa. He distinglishes three layers corresponding essentially 
to the three layers recognised by Bather (19, Zool. Rec. 1900, p. 45) ; but 
when he infers, from the relations of the nerves and lacunae, that the 
ambulacrals of Asteroids are not homologous with those of Echinoids, one 
pauses to ask whether comparative anatomy alone is competent to decide 
this vexed question. 
Turning to special groups, we find a valuable account by Ackermann (2) 
of the anatomy of Cucumaria laevigata and of its curious hermaphroditism; 
the function of the phagocytes resembles that described by Theel (298, 
Zool. Rec. 1901). The five parts of Bronn’s Thierreich edited by Hamann 
(119) complete the anatomy and embryology of Echinoidea , and include a 
careful summary by Przibram of those experiments in physiology and 
embryology for which the sea-urchin has served as corpus vile. Koehler & 
Bather (156) give a detailed description of the external anatomy of a new 
