170 P., HERBERT CARPENTER, 
Were it not for his work on the ‘Anatomy of theStarfishes,’ 
the observations of three other authors, which were published 
in 1876, would only have increased the confusion that 
already existed in this subject. This has, in fact, been 
the case with respect to the Urchins and Holothurians, 
though in a less degree, and it is now very desirable that 
the minute anatomy of both these groups should be rein- 
vestigated by the light of our present knowledge of the other 
Echinoderms. It is more than probable that the results of 
such investigation would necessitate the giving up of many 
of our present ideas concerning the nervous and vascular 
systems of these two orders. 
It will perhaps be best if we commence our studies 
with the Starfishes, which are probably the best known 
among the Echinoderms. Having acquired some under- 
standing of their typical structure, we can proceed to con- 
sider that of the Ophiurids, and finally that of the Crinoids, 
which presents many singular deviations from the ordinary 
Kchinoderm type. I shall not attempt todo much more than 
describe the actual anatomical facts, leaving almost entirely 
out of consideration any identification of particular parts 
with the structures mentioned by the older anatomists. 
This (if required) must be sought for in the original me- 
moirs themselves, a list of which is to be found at the 
conclusion of this paper. 
Figure 3 on Plate XI is a diagrammatic transverse 
section, representing the structure of a Starfish arm. On 
the left side the section is supposed to pass through a ver- 
tebral ossicle, while on the right it passes between two suc- 
cessive ossicles. The pyloric cecum (p.c.) is omitted from 
the left side for the sake of clearness, while on the right the 
genital gland (ov.) is not represented. The integument 
lining the ambulacral groove between the rows of tube feet 
differs considerably from that covering the rest of the exte- 
rior of the body. It is usually more or less raised into 
a median ridge, and consists of two principal layers, an outer 
cellular and an inner fibrillar one. The latter (figs. 3 and 
5,.) is thickest in the middle line, but thins away laterally, 
while the former (a.e.) is merely a modified portion of the 
general external epithelium of the arm (E), with which it 
is continuous at the sides of the groove. This ambulacral 
epithelium consists of columnar cells, each bearing cilia, 
which seem to pass through delicate pores in the superficial 
cuticular layer. The cells are closely packed, and their 
nuclei are situated at different heights, so as to produce the 
appearance of there being several different layers of cells 
