554 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



directed towards the anterior end of the miracidium. A redia in 

 life measured 0.14 millimeter in length and 0.04 in breadth. 



The excretory system of this distome was but imperfectly made 

 out. What appear to be two rather ample vessels uniting near the 

 posterior end at a terminal pore may be distinguished in the mounted 

 specimens. In sections these appear only as irregular spaces whose 

 connections are not clear. In a livmg specimen flattened under a 

 cover glass freely moving fluid containing refractile globules was 

 observed in branching vessels along the margins. 



The musculature of the head and neck is peculiar in that there are 

 strong muscle fibers connected with the spines. Thus in a tangential 

 section of the neck the most conspicuous muscle fibers are those 

 which run in a dorso-ventral direction. These fibers in the neck are 

 straight while the corresponding fibers in the collar become more or 

 less curved. 



There can be no doubt but that these distomes belong to the same 

 genus as the distomes from the herring gull described by Nicoll and 

 placed by him in the genus Parorchis. It would be a satisfaction 

 to me if I could refer them to Nicoll's species P. acanthus, but this 

 seems to be inadvisable on account of certain constant differences. 

 Furthermore the ova break open by a transverse fissure near the 

 larger end instead of by a longitudinal fissure. 



The differences between the adult specimens of the two species, 

 being only in minor details, might possibly be ignored. On the 

 other hand the miracidia of P. avitus appear to represent a different 

 type from that figured by Nicoll. 



In the internal anatomy my specimens resemble Braun's Distomum 

 pittaciwm from Tringa interpres as closely as the}^ do Nicoll's species, 

 but there is the same objection to referring them to that species 

 that Nicoll finds with respect to his Z. acanthus, namely, the ab- 

 sence of spines and of the characteristic collar in D. pittacium. The 

 absence of spines, it is true, is of little importance since spiaes are 

 easily lost, but the absence of the collar is significant inasmuch as 

 that structure in both Nicoll's specimens and mine is conspicuous and 

 contains characteristic muscle fibers, so that it is difl&cult to see how 

 it could become so inconspicuous as to escape observation. 



Dimensions of mounted specimens, in millimeters. 



Length 



Breadth at oral sucker 



Breadth at ventral sucker 



Greatest breadth 



Length of oral sucker 



Breadth of oral sucker 42 .36 .39 .49 



Length of pharjmx 18 .18 .22 .24 



Breadth of pharynx 22 .15 .14 .24 



Length of esophagus 42 .36 .42 .52 



Length of ventral sucker 84 .78 .71 1. 



Breadth of ventral sucker 



Distance from anterior end to ventral sucker 1.23 1.02 1.13 1.54 



