842 WINTERTON C. CURTIS 
In those sharks which were given the double dose of o. m. f. 
(table 6) not a single cestode was discovered, but as only eight 
specimens were thus treated the number of trials is insufficient 
to show that even this treatment may be regarded as always 
effective. It is perhaps too much to expect a treatment that 
will be entirely effective in every instance, nor is such a treatment 
necessary, for a stray worm or two in one shark out of a dozen 
would still give us a result good enough for practical working 
purposes. Unsatisfactory though my results are, they do, I 
think, justify the belief that a little more experimenting along 
the line of repeating the dose one or more times would develop 
a method of treatment sufficiently effective for working purposes, 
i.e., will eliminate all the parasites, except in rare instances, 
without killing too many of the sharks. If such a method can 
be found, the sharks thus expurgated could be used in a variety 
of experiments. For example, by introducing young Crosso- 
bothria into a shark one might expect to find out more than we 
now know about the rate of growth and the maturing of pro- 
glottids in the cestoda, and another point worth examin- 
ing would be the truth of the current idea that it is the inability 
of the cestode to survive in the wrong host which limits the 
habitat of a given species of parasite to a single host, or to a few 
closely related hosts. This latter point might, indeed, be in- 
vestigated by the infection of sand sharks with larval forms 
other than the ones known to occur in that host, but where the 
normal infection is so great the examination of the specimens 
would be much easier if the host was first freed of all infection. 
An insufficient supply of squeteague during the latter part of 
the second season made it impossible for me to make more than a 
few infections after the method of treatment, as above described, 
had been established. Only nine sharks were so infected and 
none of these was killed until about three weeks after the infec- 
tion had been introduced. Hence the material is wanting to 
show my transitional stages between the 8. polymorphus and the 
young specimens of Phoreiobothrium (figs. 9, 10 and 11) which 
I believe to have come from this larva. This lack of early stages 
resulted not because I chose, having only a limited number of 
