103] PROTEOCEPHALIDAE—LA RUE 103 



These cestodes vary in length from 20 to 200 mm. and their maxi- 

 mum breadth varies from 1.1 to 1.5 to 2.0 mm. Differences in the stage 

 of development and also in the amount of contraction account for the 

 greater part of this variation. The short broad head (Figs. 8, 9, 121, 

 122) is flattened dorsoventrally. Its apex may be slightly elevated or it 

 may be somewhat flattened. At the summit is a small but muscular fifth 

 sucker. The four suckers, directed forward and outward, are situated 

 at the broadest zone of the head or just anterior thereto. The breadth 

 of the head varies from 0.192 to 0.357 mm. tho the greater number of 

 heads measured 0.30-0.34 mm. In thickness the head measures 0.170- 

 0.238 mm. Such variations in dimensions are due to the states of con- 

 traction of the muscles of the neck and head. Strong contractions of the 

 longitudinal muscles of the neck and head cause the neck to dilate 

 markedly. This condition also causes the posterior parts of the head to 

 widen and thicken, and thus the suckers are directed more nearly for- 

 ward. The converse of these statements also holds. The relaxed condi- 

 tion of the longitudinal muscles and the contracted condition of the neck 

 muscles result in the narrow head. The surface of the head is smooth, 

 without wrinkles or furrows. The four muscular suckers measure 0.085- 

 0.100-0.137 mm., the fifth sucker 0.033-0.06 mm. in diameter. The 

 surface of the neck is smooth tho at times transverse wrinkles simulate 

 proglottids. The neck, usually thin, varies considerably in length and 

 breadth. It measures 0.170-0.050 mm. broad while its length varies from 

 3.0 to 10.0 mm. Its transition to the first proglottids is scarcely per- 

 ceptible. 



First proglottids are extremely variable in shape. In a strongly 

 contracted worm they are much broader than long, being about 0.34 mm. 

 broad by 0.085 mm. long. In less contracted individuals these first pro- 

 glottids may measure 0.255 mm. broad by 0.102 mm. long. Schneider 

 (1903) states that they are broader than long, nearly quadrate or longer 

 than broad. Mature and ripe proglottids show somewhat similar var- 

 iations tho in less degree. Mature proglottids in all specimens examined 

 by me were broader than long. The breadth varied from 0.935 to 1.19 

 or even as much as 1.30 mm., and the length from 0.255 to 0.340 mm. 

 Fully ripe proglottids are slightly longer in proportion to breadth. They 

 measure 1.1 mm. broad by 0.42 mm. long and in the case of the largest 

 proglottids 1.7 mm. broad by 0.85 mm. long. No end-proglottid was ob- 

 served by me. Schneider describes such a segment as being about quad- 

 rate. The number of segments varies from the few in the very short 

 worms to 150 or more in the longer specimens (Schneider). Segmenta- 

 tion is fairly evident especially when the worm is viewed with a lens of 

 low magnification, for the angles of the proglottids are rounded and the 



