ART. 7 CESTODE PARASITES OF BIRDS LINTOIST 23 



at apex, including hooks, 0.09. In lateral view the scolex may appear 

 decidedly broader than the neck, and bluntly sagittate. In dorso- 

 ventral view the anterior end is bluntly rounded and the posterior 

 end merges into the strobile, which is smooth for a short distance, 

 often as broad as the scolex, in some cases a little broader, in others 

 a little narrower, but almost invariably narrowing as proglottides 

 make their appearance. Segments appear in specimens mounted in 

 balsam about 0.28 mm. back of the scolex. As the proglottides de- 

 velop they tend to produce serrate margins on the strobile. Usually 

 they soon become squarish, then longer than broad, and more or less 

 campanulate, again shortening until they are broader than long, and 

 ultimately they may again become as long as broad. The cirrus- 

 pouch, as it appeared in a series of transverse sections was slightly 

 pyriform, measuring 0.08 mm. in length, and 0.04 in diameter in a 

 section 0.38 by 0.28. In these sections the vagina was seen to be 

 flexed in one or two sinuous folds. The cirrus-pouch and vagina lie 

 between the dorsal and ventral excretory vessels, and dorsal to the 

 lateral nerve. Diameters of section of ventral excretory vessel 0.024 

 by 0.033, of dorsal vessel 0.009 by 0.012. Diameter of ovum, outer 

 shell 0.072 by 0.065, inner 0.043 by 0.036, onchosphere 0.032 by 0.02, 

 length of embryonic hooks 0.015. 

 From the black-backed gull (Lariis marinus) : 



The scoleces of the two specimens from this host agree in all 

 essential characters with those from L. atricilla. The lateral mar- 

 gins of one of the strobiles are serrate, the usual condition, those of 

 the other are somewhat crenulate. The latter strobile is stouter than 

 the other, and the proglottides were not mature. A similar differ- 

 ence was noted in strobiles from the herring gull. A diagram of the 

 female genitalia, as interpreted from a series of transverse sections, 

 is shown in figure 63. Dimensions of the larger strobile in balsam: 

 Length 40 mm.; diameter of scolex 0.33, of sucker 0.16; length of 

 hooks 0.03; breadth of neck 0.35; distance to first segment approxi- 

 mately 0.28, length approximately 0.01, breadth 0.32; length of last 

 proglottis 0.32; breadth 0.45. Length of smaller strobile 30; diam- 

 eter of scolex 0.32, of sucker 0.15; breadth of neck 0.28; length of 

 hooks 0.03 ; length of last proglottis 0.17, breadth 0.90. 



From the Bonaparte gull {Larus iphiladelphia) : 



The average diameter of five scoleces, in balsam, is 0.35 mm., of 

 suckers, 0.18; number of hooks about 20, length 0.038. As in the 

 strobiles from the other gulls, there is much diversity of shape. 

 In some the proglottides are closely crowded at first and much 

 broader than long throughout. In others the proglottides begin 

 to lengthen near the scolex, and have a tendency to become more 

 or less campanulate. There are intermediate forms, both of larger 



