940 
urchin Melonites (Lang, ’96, ii, p. 291, Mac- 
millan edition; and Dana, ’95, Manual of 
Geology, p. 641) there are four, or in some 
genital plates five, pores, instead of one, as 
regularly in modern genera. 
The positions of the ocular plates with 
reference to the border of the anal ring are 
subject to variation. ‘The facts in the case 
are these: Ina majority of the 65 Arba- 
cias observed the plates are located exactly 
as shown in Fig. 1, where the madreporic 
plate meets its two neighbors by a long 
- joint, thus pushing the ocular plate far away 
from the border of the anal opening, as com- 
pared with the left posterior ocular plate, 
which is only slightly distant from the bor- 
der. The right posterior ocular and the 
right anterior are also less separated than 
the remaining two. Thisisthemode. The 
variations from it are on the part of the left 
posterior ocular chiefly and, in addition, of 
the right posterior, and less of the left an- 
terior ocular plates. The extreme case of 
this variation is shown in No. 5, where 
the left posterior. ocular plate. partici- 
pates in the formation of the border of the 
anal ring, as the right posterior also does, 
though in a less degree. In No. 21, the 
same variation is to be seen. Cases in 
which this form of variation takes place, 
but in a less extreme degree, are frequently 
met. No. 17 is such a case; here the 
left posterior ocular plate barely touches 
the margin; this is also seen in No. 38. 
In No. 10 this ocular does not quite reach 
the margin. The left posterior ocular 
thus shows a strong tendency to push itself 
into the analring, a tendency shown, too, 
but in a less degree, by the right posterior 
ocular and slightly by the left anterior ocu- 
lar plate. The specimen of Arbacia, figured 
by Brooks in his ‘Invertebrate Zoology ’ 
(82, p. 86), which came from Southern 
waters, shows this same variation as to 
the left posterior ocular plate. The speci- 
men of Echinocidaris (Arbacia) pustulosa, 
SCIENCE. 
[N.S. Von. XIII. No. 337. 
figured in Lang (’96, Macmillan, Comp. 
Anat., II., p. 232), shows the two posterior 
and the lefé anterior oculars all bordering 
the ring. 
In some sea-urchins (e. g., Diadema) all 
the oculars take a part equally in forming 
the boundary of the anal ring. In Salenia, 
believed to be a very primitive genus, none 
of them touchit. In Strongylocentrotus there 
is a condition between these two extremes; 
in that form the left posterior ocular and 
the right posterior ocular regularly form a 
part of the border of the anal ring, and oc- 
casionally the left anterior ocular reaches 
it. In Arbacia the corresponding ocular 
plates vary in the direction of an arrange- 
ment which is the mode in Strongylocentrotus. 
A somewhat extended study of the apical 
systems of Arbacia from widely separated 
localities, together with a similar study of 
that of some of the other sea-urchins, would 
probably be of considerable interest to stu- 
dents of variation. 
Henry LEstre OsBorn. 
BIOLOGICAL LABORATORY, 
HAMLINE UNIVERSITY, 
January 22, 1901. 
INORGANIC FERMENTS. 
Aw article on this subject appeared some- 
what more than a year ago in the Zeitschrift 
fiir physikalische Chemie by Bredig and Mil- 
ler von Berneck. Quite recently a mono- 
graph has been published by Bredig, under 
this title, containing an account of the ex- 
perimental work which he has done with 
others and also an introductory chapter on 
colloidal solutions, method of preparation, 
ete. 
The monograph begins with a discussion 
of the general properties of colloidal solu- 
tions. Graham found that colloids diffuse 
very slowly in comparison with crystal- 
loids. Pfeffer showed that colloids exert 
very small osmotic pressures, and Tam- 
mann demonstrated that colloids lower the 
