42 ILLINOIS BIOLOGICAL MONOGRAPHS [330 



HAPLOBOTHRIINAE Cooper 1917 



Strobila formed by the subdivision of the segments of a primary strobila. 

 Scolex of the latter a cylindrical, somewhat club-shaped organ bearing four 

 eversible proboscides similar in structure to those of the Trypanorhyncha ; 

 scolex of the secondary (definitive) strobila merely the shghtly modified fore- 

 most segment, provided with shallow dorsoventral depressions analogous to 

 the bothria of other bothriocephalids. An elongated neck may be said to be 

 present in the primary strobila. Segmentation of the primary strobila result- 

 ing in the formation some distance behind the scolex of a comparatively small 

 number of long, narrow segments which in turn subdivide anteriorly to form 

 the segments of the secondary strobila. Segmentation in the latter thus 

 beginning immediately behind the secondary scolex, but complete in its anterior 

 region only. Genital organs simple in each proglottis. Genital openings 

 surficial, ventral and median as in the Diphyllobothriinae. Ovary and shell- 

 gland median, respectively ventral and dorsal. Vitelline folUcles in the medul- 

 lary parenchyma, as are the testes, both within the nerve trunks. Testes 

 separated into two lateral fields by the median excretory vessel and the genital 

 organs in the median line. Vas deferens enlarged to form a large non-muscular 

 seminal vesicle before entering the cirrus-sac. Cirrus armed with minute 

 spines. Receptaculum seminis medium sized, sharply separated from the 

 spermiduct. Uterus divided into a much coiled, proximal uterine duct and a 

 large uterus-sac, as in the Ptychobothriidae. 



Tj'pe genus: Haplobothrium Cooper. 



Altho as yet comparatively little is known about the life-histories of the 

 bothriocephaHds, it has been shown that the definitive scolex and strobila 

 develop directly from the larval stage, known as the plerocercoid, which is 

 present in the intermediate host. This is certainly the " case with Ligula, 

 Schistocephalus, Diphyllobotkrium latum, Cyathocephalus truncatus and Tri- 

 aenophorus. As a matter of fact in all of these the scolex is more or less well 

 formed before the larva reaches the final host; and after that the plerocercoid 

 continues to grow and soon shows the beginnings of segmentation which mark 

 the young strobila. Consequently the wTiter feels that what in the present 

 paper is called the primary' strobila of Haplobothrium must be looked upon as 

 the true strobila, homologous to the young strobila of other bothriocephalids. 

 This is contended in spite of the fact that what was formerly considered 

 (Cooper, 1914, 1914a) to be the strobila is quite similar, apart from the absence 

 of external segmentation in its posterior region, to that of other members of 

 the order. Even tho it is provided with a very aberrant scolex region — and 

 the scolex is no more sharply set off from the rest of the larva in other species, 

 such as D. latum — the young imsegmented primary strobila may be considered 

 to be a typical plerocercoid. 



The nervous system is typical in that it consists of two chief strands united 

 anteriorly by a commissure. The relatively large size of the latter, however, 



