MR. G-. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
737 
the first thing to be affected by the nitrite, so it is the last thing to return during 
recovery. 
§ 3. Cctffein. — The effects of caffein on Sarsici may be best studied by immersing the 
animals in a saturated sea-water solution of the substance. In such solutions the 
Medusae float to the surface, in consequence of their lower specific gravity. I therefore 
used shallow vessels, in order that the margins of the nectocalyces might rest in the level 
of the water that was thoroughly saturated. The immediate effect of suddenly immersing 
Sarsia in such a solution is very greatly to increase the rate of the pulsations, and, at 
the same time, to diminish their potency. The appearance presented by the swimming- 
motions is therefore that of a fluttering nature ; and such motions are not nearly so 
effectual for progression as are the normal pulsations in unpoisoned water. This stage, 
however, only lasts for a few seconds, after which the spontaneous motions begin gra- 
dually to fade away. Soon they altogether cease, though occasionally one among a 
number of Sarsice confined in the same saturated solution will continue, even for 
several minutes after the first immersion, to give one or two very feeble contractions at 
long intervals. Eventually, however, all spontaneity ceases on the part of all the 
specimens ; and now the latter will continue for a very long time to be sensitive to 
stimulation. At first several feeble locomotor contractions will be given in response to 
each stimulus ; and as on the one hand these contractions never originate spontaneously, 
while, on the other hand, paralyzed Sarsice never respond to a single stimulus with more 
than a single contraction, these multiple responses must, I think, be ascribed to a state 
of exalted reflex irritability. After a longer exposure to the poison, however, only a 
single response is given to each stimulus ; and still later all irritability ceases. On now 
transferring th e Sarsia to unpoisoned water, recovery is effected even though the previous 
exposure has been of immensely long duration, e. g. an hour. 
An interesting point with regard to caffein-poisoning of Sarsia is, that as soon as 
spontaneity ceases the tentacles and polypite lose their tonus and become relaxed to 
their utmost, extent. This is not the case with anaesthesiation by chloroform, even when 
pushed to the extent of suspending irritability. If, however, Sarsice which have been 
anaesthesiated to this extent in chloroform be suddenly transferred to a solution of 
caffein, the tentacles and polypite may soon be seen to relax, and eventually these 
organs lose their tonus as completely as if the anaesthesia had from the first been pro- 
duced by the caffein. Moreover in this experiment the irritability, which had been 
destroyed by the chloroform, returns in the solution of caffein — provided the latter be 
not quite saturated — though spontaneity of course remains suspended throughout. 
The effects of graduating the doses of caffein may be stated in connexion with another 
species, viz. Tiaropsis diademata. In a weak solution the effects are a quickening of 
the pulsations (e. g. from 64 to 120 per minute) together with a lessening of their force. 
On slightly increasing the dose, the pulsations become languid, and prolonged pauses 
supervene. If the dose is again somewhat strengthened, the pulsations become weaker 
and weaker, till they eventually cease altogether. The animal, however, is now in a 
