OUE DOMESTICATED ANIMALS. 31 



always detect the presence of a central depression, which 

 some helminthologists are disposed to regard as a fifth or 

 supplementary sucker. The opaque character of the head 

 and neck is due to the excessive multiplication of the 

 calcareous particles, combined with a greater density 

 of the substance of the parasite in these parts. If these 

 characters be compared with those shown by the two 

 uppermost tapeworm heads, as given in the drawing, 

 a glance is sufficient to determine their correspondency. 

 The upper figure at A, showing the head as viewed 

 diagonally, demonstrates that the four large suckers 

 precisely resemble those of the beef measle ; whilst the 

 characteristic supplementary depression is somewhat 

 more conspicuously developed. I have satisfied myself 

 that this falsely so-called sucker does not strictly belong 

 to the category of cup-shaped holdfasts — at least, not in 

 the same sense as the ordinary suckers do — but it cor- 

 responds, both structurally and morphologically, to the 

 head processes of such tapeworms as are furnished with 

 retractile proboscides. It is in the tapeworms of birds 

 especially that these appendages attain the most striking 

 degree of development ; their principal function beino* 

 to furnish a powerful means of anchorage. The presence 

 of these organs often imparts a grotesque appearance 

 to the head of the tapeworm, as may be seen, for example 

 in the case of the Tcenia paradoxa, from the oyster- 

 catcher. I have figured a specimen of this worm in 

 my general treatise (p. 108). But, reverting to the 

 illustrations, the profile view of the head of the 

 beef tapeworm (fig. 8, B above) shows this spurious 

 sucker projecting beyond the middle line at the centre. 

 I may mention that, during my examinations of the 

 fresh parasite, I have repeatedly caused this organ 



