most valued of fishes that any factor influencing the life and health of 
this shad has a distinctly economic bearing. 
RELATIONS TO THE HOST 
The injury inflicted upon the host by an endoparasite such as the 
Acanthocephala assumes several distinct aspects. Of these, three are the 
most readily observed: (1) mechanical injury to the host caused by the 
parasite; (2) physiological injury to the host through interference with 
the normal functioning of organs; and (3) physiological injury due to 
toxins produced by the parasite. For the Acanthocephala the first two of 
these are the most obvious. They cling to the walls of the digestive tract 
of the host by means of sharp spines and hooks located chiefly on a 
special organ of attachment called the proboscis. These hooks, in their 
normal functioning, pierce the wall of the intestine of the host, fre- 
quently producing thereby lacerations which are discernible as inflamed 
areas even on the outer surface of the intestine. Hofer (1906 : 231) has 
called attention to the fact that with age these areas’ become calcified. 
This condition has not been observed by the present writer. In some 
instances—for example in members of the genus Pomphorhynchus—the 
intestine may be completely perforated, so that the proboscis comes to lie 
within the body-cavity of the host. Such perforation occasionally leads 
to active migration of the parasite into the body-cavity of the host. 
Through lacerations and perforation of the intestinal mucosa disease- 
producing organisms find ready access to the tissues of the intestine, and 
through the body-cavity and the blood stream reach all organs of the 
body. Thus infection is facilitated by the presence of the Acanthocephala, 
while under normal conditions the unbroken lining of the digestive canal 
would resist the entrance of the disease-producing organisms. 
Since the Acanthocephala have no trace of a digestive system they 
appropriate from the host intestine all of the elaborated food materials 
utilized in their metabolism. The effect of this loss upon the host is con- 
tingent upon the number of parasites it harbors. The writer has fre- 
quently seen fishes that were in poor flesh yield execessive numbers of 
Acanthocephala. There is no specific symptom, however, which will per- 
mit diagnosis of the presence of Acanthocephala by external examina- 
tion of the body. Frequently the digestive tract for a considerable part 
of its extent becomes packed with these worms. In such quantities they 
effectively clog the digestive system by mechanical obstruction, and at 
the sam€é time utilize such quantities of elaborated food that the supply 
available for the host is distinctly limited. The extent of injury to the 
host through toxic substances produced by these parasites has not been 
studied directly from either the chemical or the physiological point of 
view. 
ExtENT oF INFESTATIONS 
In the present study it has seemed inadvisable to attempt any 
analysis of percentages of infestation with Acanthocephala, since in many 
