NEW AVIAN TAPEWORM. 211 



border of the segment. In this stage, when it is empty of eggs, 

 it forms a narrow transversely running tube. In ti-ansverse 

 sections of a slightly older uteius, such as that which is repre- 

 sented in text-tigure 24 (p. 201), the position of this part of the 

 reproductive organs is seen to be remai-kable. If such sections be 

 examined from in front backwards, the uterus is the first part of 

 the generative system to come into view ; for, although posterior 

 in position in its segment, the uterus lies in front of the ovaries 

 and testes. In such sections it appears first of all dorsally as a 

 narrow and transversely elongated sac, not lying in the medullary 

 parenchyma, but lying within the internal and circular layer of 

 muscles which delimit the medullary parenchyma from the cortical 

 layer— the body- wall of the worm. The uteius, so to speak, splits 

 this circular layer of muscles into two layers, fibres being recog- 

 nisable both dorsally and ventrally of it. It has probably pushed 

 its way into this situation; but located there the appearance 

 given is most suggestive of a coelomic cavity lying between the 

 body-wall and a cential hypoblastic mass comparable to the 

 i-educed gut of certain simple Planarian worms (e. g. Hwplodiscus). 

 In such sections, moreover, the lumen of the uterus is seen to be 

 not quite continuous from side to side of the body. Muscular 

 fibres run across dorso-ventrally, which are of the nature of 

 strands rather than septa. These are plainly shown in the 

 accompanying illustration (text-fig. 29). Moreover, the epithelial 

 lining of the uterus is quite alone in these transverse sections, its 

 nuclei being very deej^ly stained. 



This epithelial lining is continued over the strands of muscular 

 tissue which partly divide up the cavity of the uterus. Although 

 the uterus lies, as already said, below the dorsal parietes, there 

 are here and there a few outpocketings of the cavity of the uterus, 

 spherical in form, which push their way into the thickness of the 

 dorsal parietes. Each of these contained only one or two groups 

 of ovarian and vitelline cells, and in the case of one uterus I only 

 found two of these small blind outgrowths. These transverse 

 sections also show another fact in the constitution of the growing 

 uterus, and that is its increased dorso- ventral diameter laterally, 

 both on the pore side and on the opposite side. These dilated 

 regions of the uterus were rather more liberally traversed by 

 transverse strands than the rest of the cavity. The lateral 

 widening of the uterus is also very plainly to be seen in horizontal 

 sections, where it is visible even in rather younger j^roglottids 

 than those just referred to. These longitudinal horizontal sections 

 (see text-fig. 25, p. 202) also show very well the extension of the 

 uterus on both sides of the body up to but not beyond the large 

 ventral water vascular tubes. The cavity of the uterus is thus apt 

 to be a little shorter from side to side than the space occupied 

 by the testes. On the other hand, when viewed in a series of 

 longitudinal sagittal sections, the uterus will be seen to have a 

 greater dorso-ventral extension than the space occupied by the 

 testes. In the three figures (text-figs. 24, 26, 29), which show 



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