328 DR. A. E. SHIPLEY ON [ Mar. 16, 
GENERAL DISCUSSION ON THE RELATIONS OF ECTOPARASITES 
TO THE ENDOPARASITES OF THE GROUSE. 
We have in the alimentary canal three species of tape-worm, 
two of the genus Davainea and one of the genus Hymenolepis. 
We know that tape-worms, with perhaps the exception of one 
species, pass through two distinct and different animals known as 
hosts. In one animal it lives as an adult, in the other as a larva. 
The larval host is always, sooner or later, eaten by the host of the 
adult, and then the larval tape-worm or cyst grows into the adult 
tape-worm. It was with the hope of discovering the second or 
larval host of the grouse cestodes that we began a laborious 
research on the insects and arachnids which infest the grouse. 
Unfortunately, little or nothing is known about the life-history 
of any species of either Davainea or Hymenolepis. ‘The larval or 
cystic stages of the former have in some few cases been said to 
occur in insects and in molluses; the larva of the latter is thought 
to live in an insect or a myriapod, or perhaps even more likely 
some ‘‘ water-flea ” or other fresh-water crustacean. 
With regard to these possible second hosts. We have never 
found a myriopod in the crop of a grouse, and so far we have not 
found any crustacea—though it must not be forgotten that these 
are probably so small as to escape notice. We have found one 
species of slug in the crop of a Staffordshire grouse, which 
Mr. W. E. Collinge has kindly identified for us as Arion empiri- 
corum Feérussac, a species of slug which is common on the 
Staffordshire grouse-moors. He tells me that the slug un- 
doubtedly belongs to the genus Arion, and almost certainly to 
Férussac’s species A. empiricorum, a name J. W. Taylor, in his 
‘Monograph of Land and Fresh-water Mollusca of the British 
Isles’ *, includes among the synonyms of Arion ater (.). The 
well-known difficulty of identifying slugs which have been pre- 
served and which have lost their colour accounts for the slight 
doubt that exists. Arion empiricorwm is very voracious and 
practically omnivorous; it will eat almost anything, especially 
decaying animal and vegetable matter, fungi, paper, weak and 
injured worms and slugs, and—what is interesting from the 
point of view of the grouse tape-worms and round-worms—it 
devours the dejecta of other animals. It prefers the shady places 
in moors and fields, and emerges into the open only at dusk or 
when the day is cloudy or overcast. The following parasites 
which may give rise to adult forms in the grouse have been found 
in A. empiricorwm :— 
Trematopa (Flukes) : 
(1) Cercariacum limacis Duj.7 
(2) Cercaria trigonocerca Dies.¢ 
* Leeds, part xi. p. 167. + Dujardin, Hist. nat. des Helm. p. 472. 
+ Leuckart, Paras. d. Menschen, 2nd edit. 11. p. 86. 
