SOME MAMMALIAN TAPEWORMS. 631 



length and -breadth of the proglottides differ in different regions 

 of the body and in individuals. A small example (30 mm. in 

 length) mounted in two pieces in Canada balsam showed the 

 following characters of strobilisation. The diameter of the wider 

 posterior i-egion of the body was not more than three times that 

 of the narrowest part of the neck. I made out in all 167 strobila, 

 and thei'e were not, I am convinced, many more. The first 42 

 were ver-y short, being very much broader than long. After this 

 point the diameter of the worm became greater, and the segments, 

 therefore, larger ; they appeai-ed to be longer in proportion to 

 their breadth ; but the first 31 of the series were, I believe, 

 not so. From this point, however, to the end of the body the 

 length of the segments was proportionately a little greater. But 

 throughout the series the actual breadth was really considerably 

 greater than the length. In a second specimen, of which the 

 head end only was mounted, the state of strobilisation presented 

 quite a different appearance. The first 45 segments or so were 

 quite as in the lasb specimen ; but after this point the length 

 grew veiy rapidly in proportion to the bi-eadth, and in a few seg- 

 ments no measurements were needed to assist the eye in seeing 

 that the pi'oglottides were very much longer than broad. A care- 

 ful examination of these elongated segments showed that the 

 broader hind margin which overlapped the narrower anterior 

 section of the ensuing segment was regularly crumpled, showing 

 a series of regulai-ly arranged projections, and in the middle of the 

 segment these were repi'esented by alternate furrows and elevations. 

 This looks very much like the effect of a muscular pulling out 

 of a segment from end to end. But in any case this variability 

 in the proportions of individual proglottides shows that it is 

 a difficult matter to define Tapeworms very accvirately by the 

 proportions of length and breadth of the proglottides in different 

 regions. The instances given would appear to be those of pro- 

 glottides which had been unduly lengthened through pulling 

 longwise. But I have observed instances of the contrary. In some 

 proglottides from the middle of the body there was a marked 

 transverse wrinkling, a kind of division of the segment into 

 annuli, which shows from a different point of view how difficult 

 it is to rely upon the relative dimensions of proglottides as aids to 

 the definition of a species or of a genus, as the case may be. It 

 is cei'tainly quite unsafe in the case of this Oochoristica. 



Before proceeding to the consideration of the internal organs, 

 there is one other external feature' that requires description, 

 namely, the orifices of the generative ducts. These are alternate, 

 but not regularly so. The openings are, however, as a rule, pre- 

 ponderatingly upon one side of the body. Thus in a portion of 

 one worm I found two pores consecutively upon one side of the 

 body. The next was on the opposite side ; the five following- 

 reverted to the fii'st state, and the last examined showed again an 

 alternation. In another specimen, from another worm, there was 

 one pore on oiie side, followed by three consecutive pores on the 



