| May 22, 1873] 
NATURE 
71 
make their appearance before the body-walls have com- 
pletely closed round the yolk. 
- Prof. Qwen,* indeed, goes so far as to say that the 
Orthoptera and other Homomorphous insects are, “at 
one stage of their development, apodal and acephalous 
larve, like the maggot of the fly ; but, instead of quitting 
the egg in this stage, they are quickly transformed into 
another, in which the head and rudimental thoracic feet 
are developed to the degree which characterises the hex- 
apod larve of the Caradi and Petalocera,” 
I quite believe that this was originally true of such 
larve, but from the tendency which large and important 
organs have, to appear at an early stage of embryonal 
development, the fact now appears to be, so far at least as 
can be judged from the observations yet recorded, that 
the legs of those larva which commence life with these 
appendages, generally make their appearance before the 
body-walls have closed, or the internal organs have ap- 
proached to completion. Indeed when the legs first 
appear they are merely short projections, which it is not 
always easy to distinguish from the segments themselves. 
It must, however, be admitted, that the observations are 
neither so numerous, nor in most cases so full, as could 
be wished. 
“97 
Fic. 37.— Larva of Prawn, Nauplius stage (after F. Muller). 38, Larva of 
Prawn, more advanced, Zoea stage. 
Fig. 30, for instance, represents an egg of Phryganea, 
as represented by Zaddach in his excellent memoir,t 
just before the appearance of the appendages. It will 
be seen that a great part of the yolk is still undifferen- 
tiated, that the side walls are incomplete, the back quite 
open, and the segments only indicated by undulations. 
This stage is rapidly passed through, and Zaddach only 
once met with an egg in this condition ; in every other 
specimen which had indications of segments, the rudi- 
ments of the legs had also made their appearance, as in 
Fig. 31, which, however, as will be seen, does not in other 
respects show much advance on Fig. 30. 
Again in Aphis, the embryology of which has been so 
well worked out by Huxley,t the case is very similar, 
although the legs are somewhat later in making their 
appearance. “In embryos,” he says, “ ,4,th of an inch 
in length (PI. xxxvii. Fig. 6), I have found the cephalic 
portion of the blastoderm beginning to extend upwards 
again over the anterior face of the germ, so as to con- 
stitute its anterior and a small part of its superior wall. 
This portion is divided by a median fissure into two lobes, 
* “ Lectures on the Anatomy, &c. of the Invertebrate Animals.” 
+ “ Untersuchungen uber die Entwickelung und den Bau der Glieder- 
thiere,” 1854. 
t ‘* Linnean Transactions,” vy. xxii 1858. 
which play an important part in the development of the 
head, and will be termed the “ procephalic lobes.” I have 
already made use of this term for the corresponding parts 
in the embryos of Crustacea. The rudimentary thorax 
presents traces of a division into three segments; and 
the dorso-lateral margins of the cephalic blastoderm, 
Fic. 39.—Larva of Echinocidaris, seen from above x 3% (after J. 
Muller). 
behind the procephalic lobes, have a sinuous margin. It 
is in embryos between this and ;3oth of an inch in length, 
that the rudiments of the appendages make their appear- 
ance, and by the growth of the cephalic, thoracic, and 
abdominal blastoderm, curious changes are effected in 
the relative position of those regions.” 
In Chrysopa oculata, one of the Hemerobiide, Packard 
has described* and figured a stage in which the body 
segments have made their appearance, but in which 
“there are no indications of limbs. The primitive band,” 
he says, “is fully formed, the protozorites being dis- 
Fic. 40.—Larva of Echinus, x roo. A, anus; ¥, mouth process; 3, pos- 
terior side arm; /;, accessory arm of the mouth process; a, mouth ; 
a", cesophagus ; 4, stomach ; 41, intestine ; 0, posterior orifice; d, ciliated 
bands ; /, ciliated epaulets ; c, disc of future Echinus (after J. Muller). 
tinctly marked, the transverse impressed lines indicating 
the primitive segments being distinct, and the median 
furrow easily discerned.” Here also, again, the dorsal 
walls are incomplete, and the internal organs as yet 
unformed. 
* “‘Embryological Studies on Hexapodous Insects," Peabody Academy 
Science. Third memoir. 
