58 LEUCKART, ON DEVELOPMENT OF ECHINORHYNCHUS, 
That this is really the case is shown most completely when 
an opportunity is afforded of observmg the mode in which 
the embryo performs its boring movements. In this 
manceuvre the terminal surface with its two ridges is intro- 
verted, or rather its two sides are folded towards each other, 
and brought into contact throughout their entire length, the 
points of the spines being thus disposed in a line on either 
side, from which position, in a few seconds, by a simultaneous 
opening out of the folded surface they are moved to the right 
and left in a downward, or, if the expression be preferred, in 
a backward direction. 
The parenchyma of the body is colourless and transparent. 
But at the same time there may be distinguished in it a 
firmer peripheral layer immediately covered by the cuticle, 
and which below the terminal surface forms a knob-like 
projection (regarded by Wagener as a “sac,”—perhaps a 
stomach?), and a more fluid medullary substance of a fine 
granular consistence. That the peripheral layer, notwith- 
standing its apparent homogeneousness, is contractile, is 
proved beyond doubt by the movements of the terminal disc. 
Moreover, the motions of the embryo are not confined exclu- 
sively to the act of boring. The body may occasionally be 
seen to contract both longitudinally and transversely. It 
may be seen also now and then to bend itself in various 
directions ; and in transparent specimens of Gammarus this 
mobility is manifested in the circumstance that the young 
parasites are constantly changing their place in the interior of 
their host, slowly progressing sometimes among the viscera, 
sometimes among the muscles, and migrating from the visceral 
cavity into, and even penetrating, perhaps, to the extremity 
of the appendages, whence they return to their original site. 
The only distinct structure perceptible in the interior of 
the embryo is a comparatively large (0-014 mm.) oval-shaped, 
granular mass, which occupies nearly the whole of the central 
part of the body, and is occasionally lodged in what has the 
appearance of a vacuolar space. Von Siebold, who has already 
recognised this granular mass as a constant organ in the 
Echinorhynchus-embryo, explains it hypothetically as being 
a remnant of the vitellus. Although at a subsequent period 
this body exhibits a distinctly cellular structure, it appears 
at this time to be a mere agglomeration of granules, charac- 
terised by their considerable size and strong refractive power. 
Similar granules are also found isolated here and there in 
other situations in the interior of the embryo, imbedded in 
fact in the softer internal substance, together with which, 
during the contractions of the peripheral layer, they may not 
