HERPyLI.OBITIS AECTICUS. 
389 
evidently a good deal of variation. This portion of H. cras- 
sirostr is, according to the same observer, is mm. long, 
while Hansen (3) describes H. affinis as being 3 to 4 mm. in 
length. 
The paired egg-sacs naturally vary a good deal in size accord- 
ing to the stage of development, and they may be larger than 
the body ; they are rounded or sausage-shaped, and in one 
individual flattened and leaf-like. Each egg-sac is borne 
on a strong chitinous swelling, which is somewhat shield- 
shaped, with the point dii-ected upwards ; these two structures, 
according to Levinsen, consist of concentric rings of chitin 
(Text-fig. 1, and PI. 22, fig. 2). The eggs, owing to their being 
tightly packed, are polygonal in outline. Above the bases 
of the egg-sacs are some small apertures with chitinous edges. 
I could not make out the an-angement of these as they only 
became apparent iu my specimens after they were sectioned. 
Levinsen, however, describes and figures them as four in 
number and forming an arc, in the centre of which is a small 
process previously described by Steenstrup and Liitkeu (Text- 
tig. 1). Jensen (6) figures two more similar apertures, one 
at the apex of each chitinous boss. On the ventral surface 
are two small chitinous bodies which Kroyer suggested 
might be lenses. This, however, seems unlikely, as an 
examination of the sections shows no trace of any lens-like 
structure in this, or any other region. Kroyer was probably 
misled by his assumption that the whole of the parasite was 
external to the worm, whereas it is now generally accepted 
that the visible portion is hardly one half of the whole 
animal. The diminutive males live attached to this posterior 
region close to the egg-sacs of the females (PI. 22, fig. 2). 
The external poition of the parasite is joined to the pa.rt 
lying within the host by a narrow stalk, on either side of 
which some specimens show a light-coloured area. Just 
underneath the skin of the host the stalk becomes chitinised 
and expands into a hold-fast, which is collar-shaped with 
serrated edges (PI. 22, figs. 5 and 7). 
2. Part embedded in the host. — 'This part of the 
