338 Mr. Newport on the Natural History 
portion of the yelk is included in the blastoderma, and is beginning to disap- 
pear as a separate body, measured one two-hundred-and-fiftieth of an inch. In 
the next stage (fig.27), which shows that the last portion of the yelk is in- 
closed on the dorsal surface of the thorax of the embryo Stylops (B), as 
observed by Rathke in the Crustacea, the form of the ovum is altered. It is 
slightly flattened at its sides, is oval, and measures one two-hundredth of an 
inch. The body of the embryo is now seen partially coiled on itself, with its 
abdominal portion bent under the thoracic, and with its dorsal surface next 
the interior of the shell ; it consists entirely of an aggregation of yelk-cells, 
partially inclosed in a blastodermic membrane, which completely invests the 
folded portion, the ventral surface of the future larva, but is open on its dorsal, 
being gradually closed from behind forwards to the thorax at a subsequent 
period. On the anterior portion of the membrane, which is to become the 
tegument of the thorax, three slight transverse folds Cf), which originated in 
the previous stage of organization, now form on each side three broad tubercles 
that project slightly from the surface ; these are the germs of the future legs. A 
distinct membrane inclosing the entire embryo in the shell is now visible (g). 
. In the next stage (fig. 28), the ovum has acquired a diameter of about one- 
hundred and seventieth of an inch. The membrane that invests the embryo 
is more distinct, the pedal tubercles are elongated and pointed at their apex, 
and the remains of the yelk are rapidly becoming included in the thorax, which 
is much enlarged, but is not yet closed on its dorsal surface. Ata still later 
period (fig. 29) the form is recognizable as that of the larva of Stylops. The 
ovum is more elongated anteriorly, and measures one hundred and fiftieth 
of an inch. The dorsal surface of the thorax is closed. The tubercular legs 
now have the rudiments of tarsal and tibial joints; the head of the embryo 
begins to project slightly from the thorax, the investing membranes are more 
distinctly marked, and the body exhibits a more organized and less celliform 
appearance. At a further advanced Stage (fig. 30) the ovum is still more 
elongated, and is more flattened at its sides, the investing coverings of the 
embryo being put on the stretch by the growth and extension of the body. 
Fhe ovum now is about one hundred and twentieth of an inch in diameter. 
Still later (fig. 31) it has reached to one hundredth of an inch. The legs of 
the embryo have acquired almost their proper length, the amnion which in- 
