8 
Huxley on Lacinularia socialis. 
developed many clear spaces, or vacuolae — a liistologkal pro- 
cess of very common occmrence among the lower invertebrata. 
Now these thickenings are especially obvious in two 
localities — 1st, in the prolongation of the body below the 
visceral cavity ;* and 2ndly, in the trochal disc. 
Of the former thickenings, the fom- uppermost are pro- 
moted by Professor Ehrenberg to be testes, for no other 
reason, apparently, than that, having missed the true water- 
vascular system with its bands, he knew not where else to 
find what he calls a male organ. 
Again, the thickenings (figs. 2, 3 r) in the trochal disc are 
mostly towards its lower surface and at its inferior margin ; 
they are generally four or five on each side, and are connected 
by branched filaments with that body on each side of the 
pharyngeal mass in which the band of the water-vascular 
system terminates. 
-According to Professor Ehrenberg these are all ganglia, 
and the two yellowish bilobed or cordate bodies on each side 
of the pharynx are " comparable to a brain ! " 
Nervous System and Organs of Sense.] — On the oral side 
* Ley dig (loc, cit., p. 467-8) regards the central vacuolar mass at the 
root of the tail as a peculiar gland, from which he says a duct runs down- 
wards to terminate at the extremity of the tail. The purpose of this 
organ is to secrete the gelatinous envelope. I must confess that I saw no 
grounds for this interpretation. The extremity of the tail always seemed 
to me to present a ciliated hemispherical cavity, closed above. 
t Leydig (1. c, p. 457 et seq.) criticises at length, and altogether re- 
pudiates, the mythical nerves and ganglions which Professor Ehrenberg 
has ascribed to Lacinularia. He does not appear to have seen either the 
ciliated cavity, or the body which I still venture to think is the only true 
ganglion ; but describes a very peculiar nervous system, consisting of — 
1. A ganglion behind the pharynx, composed of four bipolar cells, with 
their processes. 
2. A gangHon at the beginning of the caudal prolongation, similarly 
composed of four larger ganglionic cells and their processes. 
The latter cells are what I have described as vacuolar thickenings ; I 
could find no difference whatever between them and the thickenings in the 
disc, which Leydig allows to be mere thickenings. 
The former were not observed by me. I have not been able to repeat 
my investigations upon this point, as 1 hope to do ; for the present I must 
offer as arguments against Leydig's interpretation of the nature of the 
structures which he observed— 
1st. That the body which I describe as a ganglion is perfectly similar 
in appearance to the mass on which the eye-spots of BracMonus are seated. 
2nd. That if such an arrangement of the nervous system as that which 
Leydig describes exists, the Rotifera are very widely different from their 
congeners, and, indeed, from all known animals. 
Leydig himself, however, says, — " That these cells, with their radiating 
processes, are ganglion-globules and nerves, is a conclusion drawn simply 
from the histological constitution of the parts, and from the impossibihty 
of making anything else out of them, unless, indeed, organs are to be 
named according to our mere will and pleasure." — L. c, p. 459. 
