TAPEWORM PARASITIC IN THE STICKLEBACK, 129 
The failure of this experiment was probably due to the small 
number of Cyclops with which the fish were fed (owing to various 
causes it was difficult to get infected Cyclops at the time), the 
short time between the feeding of the fish and their dissection, 
and the small size of the larvee. 
The experiment was then repeated, particular attention being 
paid to the above points, and this time there was success. It 
began on May 27th, when 11 sticklebacks from the same pond 
were fed with about 20 infected Cyclops. The following results 
were obtained :— 
Number Larvee in Number 
Date. Dead.* each. | ITntected. 
etre We ieee eee cease 4, 0, 4, 7,1 3 
rere ee Oth sere erie es, 3 0, 0, 4 1 
a AL i ace teh gtd Lag il 2 1 
Site GOL geapcecedeose reseee 1 1 i 
July Ist 2 8,1 2 
11 28 8 
A control experiment of five sticklebacks was started at the 
same time and gave a negative result. 
In order to test the possibility of direct development, ‘an 
experiment was started on June 12th. Nine sticklebacks were 
isolated and fed with large quantities of adult proglottides of the 
Cestode ; in addition, a large number of eggs was put into 
the water. The experiment lasted until July 16th, when the 
surviving sticklebacks were dissected. None of the nine, how- 
ever, showed the slightest trace of infection, either in the liver 
or in the intestine. 
As a further test, thirteen sticklebacks from the reservoir were 
isolated and kept for about six weeks. ‘They were then dissected, 
but the only trace of infection found was a nearly adult cestode 
in the intestine of one of them. It is practically certain, con- 
sidering the heavy percentage of intection, that at least half these 
were infected at first; the worms must therefore have been 
ejected and have shed their eggs into the water. If direct 
infection occur, then the sticklebacks should have been re- 
infected, but since no infection was found, the conclusion is that 
direct infection does not take place. La Rue (11), in attempting 
to show direct development in P. filaroides from the salamander, 
failed to infect the salamander itself with eggs of the Cestode, 
although in his case the conditions were certainly not very 
favourable. 
* Both in this, and in the following experiments, a fungus (Saprolegnia ferox) 
obtained entrance to the experimental jar and killed the fish, so that the adult 
Ce:tode could not be bred. 
Proc. Zoou. Soc.—1914, No. IX. 9 
