ANATOMY, HISTOLOGY, MORPHOLOGY, AND PHYLOGENY. Ech. 31 
In Labidiaster radiosuz , Lov£n, intercalary arms are formed round the 
disc between the primary ones, and the number of rays increases with 
age. This increase is the result of the budding of new parts upon the 
disc. The colonial nature of the Asterid body is shown by the fact (1) 
that mutilated parts are always regenerated ; (2) that in a number of 
species one half of the body is always in a condition of being regene- 
rated, owing to the division of the body in two halves ; (3) that an 
arm accidentally separated can regenerate the whole animal in some 
species ; (4) that in others arms are detached spontaneously, to reproduce 
the whole body ; and (6) that the number of arms is not constant in the 
same species : all of which characters are shared also by a Hy droid 
colony. The opposition that has been established between the words 
colony and the words organism and individual is a purely theoretical 
conception, drawn from the study of higher animals. 
Pictet describes the spermatogenesis and fertilization of Strongy- 
locentrotus lividus and other Echinids. The spermatocytes divide actively 
by karyokinesis to form spermatids. The latter contain a homogeneous 
and refringent nucleus, and at the side of it a number of very refringent 
granules or cytomicrosomes. The tail of the spermatozoon is formed as 
an elongation of the protoplasm of the spermatid. The cytomicrosomes 
are derived from the last spindle of the division of the spermatocytes, 
and consist of the achromatic portion of the old nucleus. They fuse to 
form a single “ Nebenkern,” into the composition of which the polar 
body of the kinetic spindle probably also enters. The nucleus becomes 
conical, with the Nebenkern at the base of the cone. The apex 
of the cone is at first opposite the point of insertion of the tail of the 
spermatozoon, but as the protoplasm becomes used up to form the tail it 
is inserted opposite the base of the cone. The complete spermatozoon 
consists of a head, formed exclusively of the nuclear cone, an intermediary 
segment formed of the “Nebenkern,” and a tail formed of the cyto- 
plasm of the spermatocyte. The Nebenkern is not infrequently lost. 
Fertilization takes place equally well, whether it is present or absent. 
Hence fertilization takes place through the nucleus of the spermatid 
transformed into spormatozoid and nothing else. The cytoplasm 
plays no important role in the process, and the Nebenkern is cast off, 
and has no utility for the act of fecundation. \_Cf. Fol, Embryology, 
etc., infra , pp. 35 & 36.] 
Rothpletz describes the minute structure of some supposed Diade- 
matid spines from the Oligocene, which are true Echinokl spines, and not 
specimens of Ilaploporella fasciculata , as had been thought. Three plans 
of structure are distinguished in sea-urchin spines, termed by the author 
Radioli corticati, Radioli radiati, and Radioli cancellati respectively. The 
first type is confined to Cidaridce and Salenidce. The third type was 
supposed to be confined to Echinometridce, but occurs also in Arbacia 
pustulosa. The second type occurs in Echinoids generally other than 
those specially mentioned. 
Russo (l) finds that in the ovary of Ophiuroids the ova undergo a 
