ON A CESTODE FROM CESTRACION. 403 



They lie in the central or medullary region, and are thus 

 situated on a deeper plane than the vitelline glands. They 

 average about '06 mm. in diameter. Each lobe has a fine, 

 thin- walled efferent duct ; the ducts of neighbouring lobes 

 anastomose to form a network. From this network are 

 derived larger trunks, which towards the anterior end, and 

 near the ventral surface of the proglottis, combine together 

 to form a single median vas deferens (s.d.). The latter is 

 a closely coiled, widish, tliin-Avalled tube, situated in the 

 middle of the region in front of the genital aperture. Its 

 wall consists of a reticulated material with superficially placed 

 nuclei. No muscular layer was definitely made ovit, but 

 muscular fibres must be present, as in the living condition the 

 tube is observed to undergo peristaltic contractions. The 

 " prostate " cells described by various authors (see Braun, 5) 

 as occurring in certain Cestodes, are not present. This main 

 testicular duct is always packed full of sperms, and it plays 

 the part of a vesicula seminalis as well as a vas deferens. 

 It terminates by passing through the wall of the cirrus sac 

 and becoming the ejaculatory duct. The cirrus sac has a 

 wall composed of two layers of muscle. Within it, when the 

 cirrus is not protruded, lies coiled up a long tube, continuous 

 internally with the vas deferens. This tube (fig. 5) has a 

 muscular wall, consisting of an outer thicker layer of longi- 

 tudinal fibres and an inner of circular fibres. Internal to this 

 is a homogeneous cuticular layer, beset on its inner surface in 

 the outer part of the tube with numerous excessively minute 

 spinules. Outside the muscular layer is a layer of cells 

 similar to the myoblasts of the oviduct and vagina. In the 

 space between the wall of the cirrus sac and the enclosed tube 

 are to be observed numerous muscular fibres which appear to 

 run about in every direction. 



The outer end of the tube is continuous with the outer 

 extremity of the cirrus sac, and might be described as 

 invaginated within it were it not fur the circumstance that its 

 inner end is not free, but passes through the wall of the sac 

 to become continuous with the vas deferens. 



