122 s. r{OTO. 



this, liowever, T conceive to l)e due not to the :!ctn:il miion of the yolk- 

 dnct.-i, hut to tlie circninstunee th:it the pnired ])orri()n of tlie vn_o-in:i is 

 exceedingly sliort. The p:iired (hicts of the two sides finally unite 

 with eacli otlier, in most species in the median line of the hody; hnt in 

 DicJitlopliom se:^silis the point of union is displaced a little towards tlie 

 right side. In all the species the paired yolk-ducts form hy their 

 union an enlargement, which during the period of reproductive activity 

 is usually swollen to a considerahle size hy the great quantitv of 

 yolk-cells which it contains, and has received the name of ritcUiue 

 rfsrrroir. In most genera this ]ioi1ion passes without anv marked con- 

 striction into the contiguous ])arts; l)ut in Fjpihilrlla and TriMomum it is 

 usu:illy spherical in form a.nd is distinctlv set off from the other jiarts. 

 In ( hicliocofiih' and Ile.racol i/h' aUo, it passes wirhout any distinct demar- 

 cation into the antei'ior part of the yolk-ducts, l)ut is distinctly 

 set oft' from the unpaired yolk-ducts to which it gives rise (PI. XV, 

 fig. 1). The vitelline reservoir must not he regarded as a permanent 

 organ, heing observahle only when it is filled with yolk-cells. 



From the yolk-reservoii- ])roceeds the unpaired yolk-duct. This 

 is usually much smaller than the terminal portions of the ])aii'ed ducts, 

 and is therefore distinctly marked off fi'om the reservoir. In most 

 si)ecies it cither takes its rise on the ventral side of the reservoir or 

 proceeds from it directly l):ick wards, and after a course of \'arious 

 length according to the species finally opens into the o\iduct. In 

 Hexacotijlt', however, it proceeds laterally from the reservoir and unites 

 with the oviduct. In Calieotijk the unpaired yolk-duct is exceedingly 

 short, and in ALmocotiiU it is entirely wanting, the paired ducts open- 

 ing in this genus separately into the (niduct from either side. 



Where the various genital ducts come to lie in the same 

 sagittal ])lane. the yolk-duct is genci'ally situated ventrally to them, 

 hut in CdlicjlijJc, in which it opens into the seminal rece])tacle, 



