The President's Address. By Dr. C. T. Hudson. 
13 
know of no one wlio has seen such openings. Or it is possible that 
the spermatozoa may pass through the walls of the oviduct, just as 
white corpuscules pass through the walls of the capillaries. And 
though it is hardly likely that this should be their regular path, yet it 
is obvious that they are capable of penetrating the membrane, which 
covers the ovary and is prolonged into an oviduct, for they have been 
seen to attach themselves to the external surface of the ovary,* so 
that their contents must pass through the membrane to get at the 
germ. 
There remains one more organ that is waiting for a skilful experi- 
menter and observer, viz. the contractile vesicle with its lateral canals 
and vibratile tags. Various functions have been ascribed to this group 
of vessels. It has been described as a male sexual organ, as a respiratory 
organ, and as an excreting one. The last explanation is the one now 
usually given ; but there are difficulties in the way of its complete 
acceptance which have not as yet been met. 
The theory is that the lateral canals, aided by the vibratile tags, 
gradually fill the contractile vesicle with a secretion derived from the 
perivisceral fluid ; and that- the contractile vesicle, as soon as it has 
reached its full distention, discharges this fluid through the cloaca. 
Now it can be readily demonstrated that the contractile vesicle 
does discharge its contents through the cloaca,! but it is not easy to 
credit that these contents consist solely of a secretion derived from the 
perivisceral fluid. For the contractile vesicle, owing to its rapid and 
continuous action, often discharges in a minute or two a quantity of 
fluid equal to that of the whole body. Take for instance the case of 
Mastigocerca carinata. Gosse observed that the discharge took 
place twenty-five times in a minute ; and, as the volume of the vesicle 
is greater than one-tenth of the perivisceral fluid, it would follow that 
the creature renews the whole of its body-fluids at least twice in a 
minute. Is this likely ? and, if it could be established as true, what 
could the perivisceral fluid be but mere water drawn from without ? 
Secretion , at such a rate, seems impossible. What, too, shall we say 
of the great contractile vesicles of some of the Asplanchnae , filling 
more than half of the body-cavity ? Or of that of Brachionus mili- 
tarise expanding even to two-thirds ? Is it probable that they are 
filled with a secretion ? 
Moreover, that practised observer Cohn declares, that he has seen 
particles of pigment first driven away by the rush of fluid from the 
contractile vesicle, and then carried by a return current, through the 
cloaca, right into the vesicle ; while other particles, turned back by its 
contraction, were violently driven out again from the cloacal aperture. 
* Dr. Cohn and myself have seen this in Conochilus volvox. 
f By compressing a young Asplanchna Ebbesbornii , so as to check slightly the 
action of the contractile vesicle, I have caused partial contractions, each of which 
has been seen to send a plug of fluid down the oviduct to the cloaca. I have also 
successfully tried the same experiment on Hydatina senta. 
