128 MR. F. J. MEGGITT ON A 
Cypris. In all cases the animals in the control lived longer 
than those in the experimental dishes.) Moreover, no attempt 
was made to discriminate between the different species of 
Cyclops, since the species infected was not known. Under the 
most favourable conditions it is extremely difficult to see the 
eges in the host, so that, owing to the opacity of the body 
and the development of the dense black ovaries, many probable 
cases of infection have been overlooked. The results were there- 
fore as good as might be expected. 
The intermediate host is therefore a species of Cyclops, which 
Professor G. 8. Brady has kindly identified for meas C. varius 
Lilljeborg. 
In this connection it may be said that the younger Cyclops 
appear to be more easily and more heavily infected than the 
adults; the nauplii, however, are never infected. 
In addition to these culture experiments, large numbers of 
Entomostraca, Oligocheta, and aquatic insect larve from the 
reservoir have been examined at various times. In the winter 
and early spring no traces of infection were found, although it is 
quite possible that they may have been overlooked. In June, 
however, out of 117 Cyclops taken at random, 8 were found to 
be infected, and 3 out of the 8 contained larve ready to be 
transferred to the stickleback. This agrees with Kraemer’s (10) 
statement that the life-history takes place in the summer months, 
and with the fact that the percentage of adult /chthyotenie is 
erveatest at that season. The small percentage of infected Cyclops 
found can be easily explained by the fact that the 117 specimens 
examined contained examples of many species, but out of these 
only O. varius could be infected. By examining the contents of 
the alimentary canal of the stickleback, it was ascertained that 
in summer they fed chiefly upon Entomostraca, so that a very 
small percentage of infected Cyclops would be sufficient to ensure 
a heavy infection of sticklebacks. It would thus be quite easy to 
overlook this occasional infection unless one were very familiar 
with the appearance of the larve. 
In order to complete the life-eycle of the parasite, an experi- 
ment was started to infect the stickleback. This was a failure. 
A number of sticklebacks were obtained from the same pond, and 
about 20 were dissected: not one of them showed any trace of 
the parasite. Ten of them were then isolated and fed occasion- 
ally with chopped-up earthworms and infected Cyclops ; a control 
experiment was started under the same conditions, except that 
only earthworms were used for food. The experiment lasted 
from April 25th to May 16th. From time to time some fish 
died, but no trace of the Cestode was found in either those from 
the experimental jar or those from the control. On May 7th, 
for the first time, a small unsegmented Jchthyotenia was tound 
in the intestine of a dead fish; it was obviously in an exceedingly 
young stage. On May 16th the rest of the fish were dissected, 
but without finding any Cestodes. 
