255] PROTEOCEPHALIDAE—LA RUE 255 



A poorly defined neck region separates the head from the body. 

 Baird (1860) says: "No distinct neck. Anterior extremity of the 

 body very narrow." Monticelli (1899) says: "II collo e relativamente 

 lunghotto e le prime proglottidi sono come delle rughe e molto indis- 

 tinte." A. J. Smith (1908) gives a width of 0.300 mm. for the neck 

 and his drawing shows a length of 1.20 mm. Measurements of Smith's 

 material however gives a width up to 1.190 mm. Measurements of six 

 strobilas give 0.5-0.85 mm. for the length of the neck, and in these cases 

 it is probable that the measurements given are too great. The region of 

 proglottid formation begins very close to the head and here the proglot- 

 tids are very short and their boundaries poorly defined. The neck is 

 thin and flat. The first proglottids are much broader than long. As 

 they become older they increase rapidly in length. Mature segments 

 are nearly quadrate while ripe proglottids are longer than broad. The 

 moniliform proglottids, mentioned by Smith (1908), are not character- 

 istic of the species but are due to contraction states. Among the three 

 specimens which he sent to Professor "Ward was a short one which had 

 these peculiarly contracted proglottids. The longest and most perfect 

 specimens had no segments of this character nor were such proglottids 

 observed among the specimens of the other lots. Ripe proglottids meas- 

 ure 1.70-2.30 mm. in length by 0.65-1.09 mm. in breadth. 



The genital anlagen appear very early in the chain. In fact they 

 are to be seen in all but the youngest proglottids. The genital aperture 

 is irregularly alternating. It is situated near the middle of the margin 

 of the segment. The vagina and the cirrus open into the common geni- 

 tal sinus, the vagina being either anterior or posterior to the cirrus- 

 pouch. A genital sinus can scarcely be said to exist. Under favorable 

 circumstances the sinus may be seen to be 0.020-0.030 mm. deep. This 

 shallow sinus is easily overlooked. The opening of the vagina is some- 

 times dorsal to the cirrus-pouch but the writer is not prepared to say 

 that it always occupies that position. Monticelli (1899) thinks that the 

 vagina normally lies above the cirrus-pouch and that when it is found 

 anterior or posterior to the same it has been displaced by pressure. 

 From work on this species and also on several other species in which 

 the vagina may lie in either the anterior or posterior position the writer 

 is convinced that pressure has nothing to do with this variation. The 

 preparations studied have all been made without compression, yet the 

 vaginae alternate irregularly in position. Sections in a frontal plane 

 through developing proglottids of O. lonnlergii show the vaginae some- 

 times anterior and sometimes posterior to the cirrus-pouch. They de- 

 velop in those positions which they hold in mature and ripe proglottids. 

 A careful examination of toto preparations of C. gerrardii and of sev- 



