64. LEUCKART, ON DEVELOPMENT OF ECHINORHYNCHUS, 
the entire body may be distinguished a somewhat ventricose 
oval trunk, containing the reproductive organs, whose sexual 
differences are now very manifest, suspended by the ligament, 
and a much contracted cylindrical neck, mclosing and almost 
entirely occupied by the proboscis-sheath with its contents. 
In worms of a large size, even at this stage, the extremity of 
the neck, which corresponds to the anterior vesicular expan- 
sion, or proboscidian vesicle before described, but which at 
this time has become much contracted, and transformed into 
a slender muscular apparatus (m. retractor proboscidis), 1s 
prolonged in the form of a distinct though sma!l capitulum. 
The anterior border of the proboscis-sheath is inserted into 
the neck of this capitulum, in which, notwithstanding the 
absence of the hooklets, even now the future proboscis can- 
not fail to be recognised. 
As growth continues, however, the connection between the 
muscular sac and the enveloping body becomes closer and 
closer. At first there exists between them a continuous 
interspace filled with the remains of the fluid parenchyma, 
which is so abundant in the embryo, and this parenchyma, 
with its yellow granules, may be seen to be propelled in 
any direction, in obedience to the contractions of the body, 
but, by degrees, this movement becomes limited to certain 
spots, and confined more and more to narrow passages. In 
other words, the muscular membrane and external layer con- 
tinue to grow more and more together, in consequence of 
which the original space is transformed into a system of inter- 
communicating canals. 
T must also mention that the motions of the worm, after 
the shedding of. the embryonic cuticle, become not only 
weaker and more limited in extent, but also gradually assume 
a different character: In place of the earlier creeping or 
crawling movement, will now be remarked nothing but still 
slower oscillatory motions in the extremities of the body, 
and more or less extensive constrictions, limited for the most 
part to the trunk, and dependent, doubtless, upon the action 
of the newly-formed muscular walls, although their histo- 
logical development has at this period made but little pro- 
gress. 
When the worm, by continued growth, especially of the 
genital organs, has acquired a length of about 4 mm., the 
appearance of the hooklets marks its entrance into the last 
stage of development. The hooklets arise first on the summit 
of the head, but it is very remarkable that they do not sprmg 
from the outer cuticular tunic, but from the inner membrane, 
which might be regarded as the limitary layer of the original 
