21] PROTEOCEPHALIDAE — LA RUE 21 



more than a few millimeters long and less than 1 mm. broad, while in 

 others it may attain a length of 60 or more centimeters and an extreme 

 breadth of 2 to 4 mm. Such extreme size is infrequent even for the large 

 species. Many of the species of Proteocephalus are thick and fleshy 

 while a few of them are thin and flat. So also are the known species of 

 the family Monticellidae. Segmentation may be evident or obscure. 

 Perhaps in no species is it as evident as it is in some species of Taenia. 

 The proglottids are usually without sharp posterior angles and they are 

 attached along their entire width. Transverse intersegmental furrows 

 if present are shallow. 



The youngest proglottids are very indistinct and are distinguished 

 in stained preparations as faint cross bands of alternate dark and light. 

 These are darkly stained areas of rapidly differentiating parenchyma 

 alternating with the unstained future septa. Almost without exception 

 the young proglottids are much broader than long. The reverse of this 

 is true only when the anterior part of the body is in an extremely attenu- 

 ated condition. As the young proglottids develop they increase in 

 length and breadth, tho the length usually increases more rapidly than 

 the breadth. The transition from young to mature proglottids is grad- 

 ual. Mature proglottids are those in which the sexual organs have at- 

 tained maturity and egg production is about to begin or may just have 

 begun. Such proglottids are usually broader than long or quadrate. 

 The length is much greater than in the young proglottids. Mature prog- 

 lottids are the best ones in which to study the greater part of the genital 

 system tho of course a study of the uterus must be made from the ripe 

 proglottids. 



Those proglottids in which egg production is well along or complete 

 are spoken of as ripe proglottids. The uterine pouches are full of eggs 

 and the ventral openings are preparing for their discharge. Ripe 

 proglottids are frequently longer than broad tho the reverse is not un- 

 common. They are normally considerably larger than mature proglot- 

 tids. In them the vitellaria and testes may be greatly reduced in size or 

 almost obliterated by the great mass of eggs in the uterine pouches. An 

 end-proglottid is frequently present. This should be defined as the first 

 proglottid to be differentiated from the growing zone of the neck. It 

 still retains certain of the characters of the posterior end of the plero- 

 cercus which is not lost in the passage of the young tapeworm through the 

 stomach of the host. It is pointed posteriorly and has at the tip a 

 median excretory pore through which the excretory products are dis- 

 charged. Just anterior to this pore, in some species, is a contractile 

 bladder. In the species examined by the writer a number of end-proglot- 

 tids have been found; some of these contained eggs and so are to be 



