ART. 7 CESTODE PARASITES OF BIRDS LINTON 21 



eight scoleces from Lants atricilla, mounted in balsam, gave a length 

 of 0.22 mm. and a breadth of 0.32. The average diameters of the 

 suckers on these scoleces were, length 0.15, breadth 0.14. As a rule 

 the suckers are nearly circular, the length often approximating that 

 of the scolex, especially when the rostellum is retracted, and the 

 breadth approximately one-half the breadth of the scolex. The 

 rostellum is slender, cylindrical, and slightly enlarged at the apex, 

 which is surmounted by a crown of about 20 hooks. These appear 

 to be arranged in a single circle, but in specimens with the hooks in 

 favorable position for showing the arrangement they may be seen to 

 be in two circles, placed very near together, and with the hooks all 

 practically of the same size. The hooks have long dorsal and short 

 ventral roots and slender, slightly curved blades. Most of the hooks 

 in my mounted material are characterized by having a central air 

 space throughout the greater part of the length. The length of the 

 hook is about 0.038 mm. The sheath of the rostellum is muscular, 

 more or less fusiform, and, when the rostellum is retracted, reaches 

 a little way back of the posterior edge of the suckers. Measurements 

 and further details are given in descriptions of material from the 

 several hosts. 



Strobile. — The maximum length of formalin specimens is about 

 140 mm,, and the maximum breadth about 2 mm. ; a maximum length 

 of 75, and breadth of 1.5 or less, is more usual. 



The following description of the strobile is based on material 

 from L. atricilla, and is in practical agreement with notes made on 

 material from other gulls. Further details will be found in the 

 records made of material from the several hosts. There is a short 

 neck, which is usually a little narrower than the scolex; measure- 

 ments of the eight strobiles in which the average breadth of the 

 scolex was 0.32 gave the average breadth of the neck 0.29, distance 

 from scolex to first distinct segments 0.56, length of first segments 

 0.014, breadth 0.23. In most cases near the scolex the segments are 

 much broader than long. They then usually lengthen rather rap- 

 idly so that at a point 2 mm., or less, from the scolex they are as 

 long as, or longer than broad. The proportions of the proglottides 

 may vary considerably in different parts of the strobile. Thus, in 

 a mounted specimen measuring 75 mm. in length, about 1 mm. from 

 the scolex the length of the proglottides was about 0.028, the breadth 

 0.30; 2 mm. from the scolex, length 0.11, breadth 0.22; 5 mm. from 

 the scolex, length 0.21, breadth, 0.13 at posterior end, 0.11 at anterior 

 end of proglottis; at 30 mm. from the scolex, length 0.52, breadth, 

 anterior 0.18, posterior 0.32; 40 mm. from scolex, length 0,45, breadth 

 0,50, 50 mm. from scolex, length 0.63, breadth 0.63 (variable, as for 

 examples, the proglottis in front of this, length 0.67, breadth 0,56; 



