THE SCOLEX POLYMORPHUS 821 
a hand net and placed in the trough ventral side uppermost. 
Upon fastening its lid, the holder was at once raised to a conve- 
nient position and the operator could then quickly introduce any 
desired object into the mouth cavity. In feeding, the jaws were 
pried open, a piece of food placed in the mouth and after being 
guided past the gill arches was thrust down the oesophagus by 
means of a billet of wood. The oil of male fern and the calomel, 
used in the attempts to rid the sharks of their previous infection, 
were given in gelatin capsules having a capacity of 2cc. These 
were placed in a piece of galvanized iron pipe, which had been 
pushed down the oesophagus until it reached the stomach, and the 
capsule foreed down the pipe with a small wooden rammer. 
This proceeding, or the giving of food, could be accomplished 
with comparative rapidity and the sharks were often back in the 
ear within two or three minutes after being taken out. There 
was no sign of the regurgitation of food or drugs, though the 
bottoms of the cars were carefully inspected during the hours 
just after treatment, and both food and drugs were found in the 
digestive tracts of specimens which happened to be examined 
during the first few days. There can, therefore, be no doubt that 
both remained in the stomach when once introduced. Further 
details of methods used are given at the appropriate places 
throughout the paper. 
THE NATURE OF THE SCOLEX POLYMORPHUS 
Before describing the experiments in which the larval cestode 
known as the Scolex polymorphus was used to infect the sand 
shark, it may be well to offer a word of explanation regarding this 
form. The name 8S. polymorphus has been applied by Linton to 
a cestode larva found in a considerable number of fishes from the 
Wood Hole region. While most abundant in the squeteague 
(Cynoscion regalis) and the common flounder (Paralicthys den- 
tatus), he has found it in varying numbers in some twenty-eight 
other teleosts, the list of which is given on page 413 of his 1901 
report. This larva, which I have represented in figs. 1, 2, 3,, 4, 
12 and 13 of this paper, is frequently met with in a stage slightly 
