Habits and structure of Cotylaspis insignis Lerpy. 209 
twenty-nine acetabula is the mode, there are variations from it. 
29 was found in 58 instances, nine cases varied from it. The type 
and the variations are shown in the annexed text-figure. Of these b 
was found in 3 cases, c in three cases and d, e and f each in one 
case. From them we see that in six cases the median row had only 
eight acetabula, in three cases (b) the end acetabulum of the outer 
row was doubled, increasing the total number to thirty. In d the 
end acetabulum of the outer row is not developed, reducting the 
total number to twenty-five. In e the same acetabulum is doubled, 
and the whole number is twenty-seven. In f there are twenty-eight 
acetabula. The arrangement at the anterior end is thus found to 
be constant but at the posterior end is variable. Porrter reports 
a different number of acetabula for C. lenoiri, namely twenty-five, a 
median row of seven, and two outer acetabula opposite the last of 
the median now, as on one side in my case f. His species differs 
from C. insignis at the hind end only, and in a manner in which 
C. insignis is found itself to be subject to variation. I regard this 
fact as showing a close kinship between these two species, but do 
not attach enough importance to it to justify regarding the two as 
specifically identical. 
There is a row of minute orifices (Fig. 5, 6, 9) all the way 
around the margin of the ventral sucker at the junctions of each 
two acetabula. They are the openings of certain organs, marginal 
organs, the homologues of which are found in other members of the 
family, and which will be considered later in this article. 
STAFFORD (1896) describes a cavity in Aspidogaster to which he 
gives the name “cervicopedal pit”, located between the “neck” and 
the “foot”, which runs backward some distance. A structure which 
is possibly related to this is described by NickERson (1899) as oc- 
curring in Cotylogaster occidentalis, where the front half of the body 
is “capable of being retracted telescopically, into the body proper”. 
No such pit is found in Cotylaspis, as shown by sagittal sections 
(Fig. 8), and there is no power of retracting the front part of the 
body like that of Cotylogaster. 
e) The Cuticle. 
An unusually heavy cuticle envelops the entire worm and is 
infolded at all the orifices, viz., those of the mouth, excretory organs, 
marginal organs of the ventral sucker and the reproductive organs 
(Figs. 6, 7,8). It is thickest dorsally on the body, 15 «, and thinnest 
Zool. Jahrb. XXI. Abt. f. Anat. 14 
