LEUCKART, ON DEVELOPMENT OF ECHINORHYNCHUS. 63 
and more the aspect of a cervical appendage to the proper 
body. 
e the meanwhile, the worm has gradually become so large 
as almost completely to fill the interior of the embryo. But 
notwithstanding this, the latter has undergone no change, 
except in the continued multiplication of the yellow granules 
beneath the contractile cortical layer, and the appearance 
of vesicular cells (0°007 mm.) im that layer. It contracts 
and stretches itself as be’ore, and is in continued motion 
within its host. Its movements, however, appear on the whole 
to be less effective than they were, owing to its free move- 
ments being interfered with by the worm in its interior. 
Having traced the young Hchinorhynchus up to this stage 
of development, I expected every moment to witness its 
liberation from the original embryo. But I was again 
astounded to find that this liberation never took place. The 
embryonic body, with its cortical layer and yellow granules, is 
persistent during the whole of life, and gradually becomes closely 
attached to the worm, which is developed from the metamor- 
phosis of the nucleus in the manner above- described. It is 
transformed, in fact, into the tunics external to the muscular 
sac, and which from their thickness and granular texture, as 
well as from the existence in them of a distinct vascular system, 
as has been long known, constitute one of the most striking 
characters of the Acanthocephali. 
Properly speaking, however, it is not actually the whole 
embryonal body which is transformed into this tunic. The 
original cuticle, together with the spines, is thrown off, as 
soon as the Hchinorhynchus occupies the whole interior of 
the embryo. But this shedding of the cuticle is in any 
case of but little importance, and scarcely to be com- 
pared to the mode in which Nemertes slips out of its 
Pilidium. 
It should, moreover, be remarked, that I have not directly 
observed the shedding of the embryo-cuticle, and only 
conclude that it takes place from the circumstance that 
Echinorhynchi of about 1 mm. in length no longer present 
the embryonic form of head, and are not furnished with 
spines. The primary embryonic body, which at first might 
be regarded as, to a certain extent, an independent animal, 
after the loss of the original cuticle accommodates itself 
more and more accurately to the form of the Echinorhynchus. 
And this is the more remarkable when it is considered that 
the growth of the latter from this time proceeds at a very 
rapid pace. 
As at an earlier period in the inclosed worm, so now in 
