STRUCTURE OF PROGLOTTIDES. 91 



vaginal branch, and more towards the middle of the segment, in 

 the form of lobate glands, with csecal tubes and a transverse 

 efferent duct ; they do not, however, contain the ordinary con- 

 tents of gerraigenes, but small, refractive, displaceable, homo- 

 geneous vesicles, destitute of both nucleus and membrane. They 

 are, consequently, only places for the production of germinal 

 vesicles. We find as many pairs of germigenes in one segment 

 as there are vaginae and porigenitales. The vitellogenes (cuta- 

 neous glands of Van Beneden), which are situated more peri- 

 pherally, are smaller or larger, transverse, csecal tubes, united 

 by a central longitudinal stem, with fine, coherent, fatty granules 

 and efferent ducts, which cannot be traced as far as the uterus. 



The uterus is a simple, median canal, which is gradually de- 

 veloped from below upwards, where alone it exhibits dilatations, 

 which become elongated and branched, and are developed at the 

 expense of the other sexual organs. The testes, which are readily 

 recognisable in the younger segments, are clear, roundish vesicles, 

 reaching 015 millim. in diameter, placed at the side of the 

 uterus, especially in the upper part of the body, close to and 

 beneath the germigenes. Vasa efferentia, which are probably 

 present, although perhaps only temporarily, are never distinctly 

 visible. When the seminal duct begins to fill, the testicular 

 vesicles dehisce. The seminal duct, a repeatedly contorted canal, 

 running transversely through the middle of the segment, has 

 already been referred to. Care must be taken to avoid regarding 

 empty branches of the uterus as testes. The contents of these 

 branches are small, clear, seminal cells, and afterwards simple, 

 very long, capillary seminal filaments. 



The maturity of the segments commences at various distances 

 from the head in different species. We first of all see a trans- 

 verse streak in the middle of the segment (vagina and penis) ; 

 then the separation of this streak into two canals ; then the 

 commencement of the testes and germigenes ; then that of the 

 vitellogenes ; afterwards that of the uterus ; and lastly, the 

 seminal filaments, after the transfer of which the development of 

 the embryo begins. 



As regards the development of the eggs and embryos, we shall 

 follow Leuckart's statements. Before him nothing had been 

 made known on this subject, except by Kolliker ( Muller's 

 ' Archiv/ 1843, p. 91), and also by Van Beneden, who speaks of 

 a segmentation of the vitellus. Before the filling of the seminal 



