ON A NEW GENUS OF BIRD-CESTODES. 143 



other vesicles are situated more anteriorly and lie in the 

 medulla on the side remote from the pore-bearing edge and 

 just internally from the excretory vessel of the correspond- 

 ing side (fig. 4). By the time that the ovary is matured, 

 the testes have already begun to abort. 



The vas deferens is a fairly well marked tube also lying 

 on side remote from the pore-bearing edge. It is rather 

 wide and somewhat coiled. After passing forwards close 

 to the excretory vessel it then travels across the segment 

 to enter the cirrus sac. Just before its entry there may 

 be a slight enlargement representing a vesicula seminalis. 



The cirrus sac is a very large, powerful organ, at whose 

 inner end is a strong mass of muscular tissue constituting 

 a cirrus-retractor muscle. One can scarcely differentiate 

 between a cirrus and a cirrus sac, though I am using the 

 latter term to distinguish that part which lies nearest the 

 genital pore and is not eversible. The cirrus appears as a 

 comparatively long strong walled structure forming the 

 continuation of the vas deferens. Its walls are beset with 

 a dense covering of bristles whose points are directed out- 

 wards while the cirrus is at rest, but when the organ 

 becomes everted these spines come to lie in such a way 

 that their points are backwardly directed. Each spine is 

 then seen to be comparatively large and strong and to 

 resemble a rose thorn in shape, its base being about 3*5/* in 

 diameter and its length 10/*. On the swollen basal part of 

 the cirrus, there are a great number of closely set spines 

 of the same shape but of larger size than those on the other 

 part, their measurements being about 7/* at the base by 

 17/* in length. There is no appearance of special spines 

 such as those described as occurring at the base of the 

 cirrus in Acanthocirrus. Perhaps one should consider the 

 greatly elongated muscular structure which forms a narrow 

 sheath around the inner parts of the retracted cirrus as 



