TAPE-W0R.AI8 OF THI-: SUC-FAMILY AYITELLINli\.4>:. 369 



interior end of tlae receptaculuni seiniuis arises the canalis 

 seminalis (Befruchtungskanal — fertilisation duct), which, how- 

 ever, soon branches, sending one arm, the oviduct, to the 

 ovarium, the other arm, tlie uterine duct, to the uterus. 

 Fertilisation of the eggs probably takes place at the point of 

 junction of the three ducts, as one canuot observe spermatozoa 

 penetrating into either the oviduct or the uterine duct. The 

 uterus originates as a simple, hollow, transverse tube, but 

 fills with cells soon after the arrival of the ova, cells derived 

 from the uterine walls completely surrounding and embedding 

 the eggs. 



At the same time the male sexual organs consist of a cirrus, 

 which opens straight into the vagina ; the vas deferens forms 

 several twists and turns within the cirrus-pouch (fig. 4). 

 Just before entering the cirrus pouch the vas deferens is 

 considerably swollen with spermatozoa, forming a kind of 

 vesicula seminalis. The vas deferens runs straight across the 

 dorsal side of the segment, l)eing dorsal to all the other 

 genital organs, to the nerve and to the excretory canals. 

 The testicles lie near the transverse axis, in four groups of 

 from three to seven testicles, one group being lateral and one 

 median to each ventral canal. 



The changes that follow as the segments proceed from the 

 anterior end of the strobila to the posterior end are, first the 

 disappearance of the ovary and oviduct, then of the canalis 

 seminalis, then the testicles disappear. The uterine duct, 

 the receptaculum seminis and the cirrus pouch with the 

 vagina remain long after their function is past. When the 

 ovary is disappearing the paruterine organ begins to 

 develop J finally all the eggs are enclosed in the paruterine 

 organ (fig. o). 



In their first anlage the cirrus-pouch and the vagina 

 appear to have a common origin in a clump of dai'k-staining 

 nuclei which collect near one of the lateral margins. Later 

 on this clump splits into two masses, which are surrounded 

 by myoblasts (fig. 44). In the middle of each of these 

 masses a central core of cells differentiates, those which are 



