Packard.] 318 [May 2, 
<k'sci-il)e<T by Metschnikoft" ' ; :ui(l an aiiiilogous struct.uiH' on the 
ceplialotUorax of tlie embryo of phalangids observed by JJall)iam". 
The egg-shell burster of Pulex canis (also observed by Kinickel, 
and afterwards by Balbiani) was seen in the egg just before hatch- 
ing. It is a thin vertical plate like the edge of a knife, situated 
in the median line of the head very near the posterior end and is of 
the form represented in Figs. 3 and 4, being somewhat cultriform, 
the upper edge slightly hollow, the anterior end being slightly 
turned up. Unfortunately the apparatus was not seen in motion, 
nor the muscles moving it, if any such exist. So far as I could 
see, it is a fixed chitinous, keel-like spine which, however, was not 
seen to rise above the surface of the head, though it is evident 
that it is situated at just the point on the head where it would 
come in contact Avith the egg-shell, and it was evident that the 
larva, by rubbing its head back and forth, would produce a slight 
split in the shell, and cause it to burst asunder. 
In the larva just before hatching the plate is no more hard and 
chitinous than the rest of the head, but in another larva a little 
older it was harder and with more chitine than in the rest of the 
head. 
It will be seen by Burgess's figure that he also pei-ceived this 
structure, and represents the upper edge as slightly hollow. He 
drew no muscle. The organ was previously observed but not 
represented by Bonnet in his figure of the larva of Sarcopsylla. 
Later on in larval life it probably disappears, possibly after the 
first molt, though we know nothing of the process and number 
of molts in the fleas. 
The general shape of the head is more like that of Gyrinus, 
Philhydrus, etc., than of the Mycetophilidae or other dipterous 
larvae, being conical, longer than broad, and on the under side the 
meutum or mental region is large, extending back to near the end 
of the head and forming a long scutellate area. 
There are no traces of eyes. The labrum is large and of the 
normal shape, rounded in front. 
The antennae (Fig. 4, 5, ant) are three-jointed, rather long 
and slender, being about one third as long as the head. On the 
short basal joint, surroundin_g the base of the long, rather thick, 
second joint are six short spinules ; the third joint is very slender, 
> Zeitschr. fiir wiss. zool., 2-4, p. 263, taf. 25, f. 18, 19, 1873 ; ibid, 25, taf. 20, f. 7, u. 
taf. 21, f. 11, 12, u, 1875. 
