336 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
those of the youug are often more varying and complicated than those 
of the adult. 
In the mesentery we have to distinguish a dorsal part divided into 
two, the upper of which depends from the pharynx and oesophagus, and 
represents the oesophageal mesentery of Echini, and the wall of the 
liydrophoric sac of Starfishes ; there are lateral and ventral parts and 
an intermediate or internal mesentery, the development of which is 
proportional to the depth of the intestinal loop. The endothelium of 
tbe general cavity contains stomata. The “ aquopharyngeal bulb,” 
which is situated at the superior extremity of the digestive tube, con- 
tains, in the Pedata, an axial part — the pharynx, and a peripheral part 
which is formed by the calcareous corona and the central parts of the 
aquiferous apparatus. These two parts are separated by the circum- 
pharyugeal sinus, which is an appendage of the general cavity. The 
upper extremity of this sinus forms the circumbuccal sinus. 
The aquiferous system of the Pedata is similar to that of Echinoids ; 
it is made up of a ring situated at the base of the pharynx, to which are 
appended the sand-canal or canals and the Polian vesicles ; each of the 
radial vessels given off from it consists of three portions — one dilated, 
one coronal, and one ambulacral. The two latter have, at their sides, 
more or fewer orifices which establish communication between the 
vessel and the ambulacral tubes ; all these orifices are provided with a 
valve. The tentacles are ambulacral tubes depending from the coronal 
portion, and adapted to special functions. The aquiferous apparatus is 
essentially locomotor, and is entirely distinct from the amoebophorous 
system. The endothelium of the former system, as well as that of the 
general cavity, only adheres to the subjacent layer by filiform prolonga- 
tions, and thus a subepithelial lacuna is formed. 
In addition to the nerve-trunks common to them and Echini, 
Holothurians have five internal ambulacral bands, the upper ends of 
which bifurcate and bend inwards to the aquopharyngeal bulb. The 
superficial nerve-plexus of Echini is represented by a deep nervous 
plexus. The amoebophorous system, like that of Echini, is formed by a 
system of free and one of connective lacunae. The former is composed 
of a circumpharyngeal ring, of an internal marginal lacuna, and of an 
external marginal lacuna, with which a genital lacuna is connected ; 
there are also five radial lacunae. The second system is placed in the 
median zone of the wall of the body, of the digestive tube, and of the 
gonads, in the axis of the circumpharyngeal and circumcloacal tracts, 
and in the mesenteries. The dendritic organs are, primarily, hydrostatic 
in function, but are also respiratory and excretory, and probably serve 
also for amoebocystogenesis. The Cuvierian organs are glandular, and 
not defensive, as has been asserted by various writers. 
Excavations by Sea-Urchins.* — Mr. J. W. Fewkes thinks that the 
excavations sometimes made by Strong ylocentrotus drobachiensis on the 
coast of Grand Manan are made by means of its teeth and spines, com- 
bined with motions of the animal produced by waves and tide. Though 
primarily protective, the holes also serve to contain a sufficient quantity 
of water when the animal is uncovered. 
Amer. Natural., xxiv. (1890) pp. 1-21 (1 pi.). 
