214 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
liis account of the Hulothurians. After finishing the subject of geo- 
graphical distribution, which he began in a previous part, and telling 
us that the greatest depth from which Hulothurians have been taken 
is 2900 fathoms, he passes to physiology and oecology ; the functions 
of the several organs and systems are first dealt with, and afterwards, 
among others, locomotion, nutrition, reaction to strong stimuli, regen- 
eration, length of life and rapidity of growth, enemies, protective 
arrangements and parasites are discussed in detail. 
The young are sometimes cared for by the parent, and in three 
different ways ; the coelom serves as a brood-cavity in Phyllophorus 
urna, Synapta vivipara, and Chiridota rotifera ; the eggs and young are 
attached to the back of the mother in Cucumaria crocca, and Psolus 
ephippifer ; the eggs are placed in special brood-pouches, formed by 
invagination of the skin in Cucumaria Jsevigata and C. minuta. The 
only llolothurian that is known to swim is Slichopus natans, which Sars 
observed moving like a Planarian or a Leech. 
After detailing the uses of Holothurians to man, and the little that 
is known concerning their palasontology, the author concludes with a 
discussion of their phylogeny ; the tree now given does not differ from 
that which we have already reproduced.* He concludes that, on 
the whole, the existing Aspidochirotas and Dendrochirotas represent the 
typical Holothurians ; though they have, it is true, diverged from the 
primitive form, they have remained more like it than the Elasipoda, 
Molpadiidae, and Synaptidas ; these last are a very old group, but at 
the same time the one that is most divergent from the primitive form. 
The author criticizes the views of those who have held different views 
from these as to the interrelations of the groups of Holothurians. 
Physiology of Nervous System of Echinoderms.f — Drs. J. Demoor 
and M. Chapeaux have made a number of experiments on Asterias 
rubens. With regard to the general anatomy of the nervous system it 
may be said that, while it is diffuse in character, a tendency to cen- 
tralization is shown in the condensation of ganglionic elements at 
definite points. With regard to their functions tho authors’ experi- 
ments lead them to conclude that the co-ordinated movements which 
cause the turning of a starfish laid on its back are reflex actions depen- 
dent on the condensed nervous system ; the intervention of the circum- 
oral centres increases the rapidity with which this action is performed. 
The authors have studied the curious property of self-mutilation or 
autotomy possessed by some Starfishes, and conclude that, so far as 
the motor reaction is concerned, autotomy is a reflex action, the centre 
of which is placed in the nerve-ganglion of the arm. The intensity 
of the phenomenon is a function of the number of ganglia which act 
in concert. 
The tentacles exhibit movements of extension and of retraction ; 
the latter is the result of a simple reflex action, the irradiation of 
which in the condensed nervous system is proportionately more rapid 
as it occurs closer to the circumoral cord ; the influence of the perieso- 
phageal centres is manifested in this phenomenon. Extension is a reflex 
* This Journal, 1891. p. 478. 
f Tijdschr. Nederl. Dierk. Vereeu., iii. (1S91) pp. 108-G9 (1 pi.). 
