262 PIIOCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
organs. It is very difficult to identify them satisfactorily, but ap¬ 
parently they belong to the pharyngeal (sympathetic) ganglionic 
system, and I have called them ganglia allata (see Heymons, 95 , 
p. 49), inasmuch as they do not arise from the dorsal stomodeal wall, 
but probably from the outer ectoderm, whence they migrate dorsally 
to the position they finally occupy. In other insects in which these 
or at least similar ganglia appear, they originate as thickenings or 
invaginations of the ventral body-wall in the neighborhood of the 
maxillae, and migrate dorsally either to fuse with each other in the 
mid-dorsal line just above the stomodeum (Forficula) or to remain 
separate (Gryllus). In Melophagus, since the head-fold and the 
stomodeum occupy the dorsal portion of the germinal band, these 
ganglia probably do not have a ventral, but rather a lateral, origin 
(PI. 3 , Fig. 18, gn. ala.). But, as will be seen in subsequent stages, 
they migrate to a position immediately beneath the dorsal body- 
wall, fuse together, and enter into relations with important pharyn¬ 
geal organs. 
No neuroblasts appear in any part of the nervous system at 
this early stage of development, the cells being spherical bodies 
of nearly equal size. The germinal band has not, in the stage just 
discussed, grown over the dorsal side of the animal (except, of 
course, on the head- and tail-folds) to complete the formation of the 
back. 
In the next stage the stomodeum (PI. 3 , Fig. 22, stmel.) has 
reached the forward pole of the body. The cephalic discs have 
also changed their positions and migrated farther forward. The 
median disc is now situated immediately ventrad of the mouth 
opening (else. ee. m.) ; the paired discs have moved still farther 
forward, and are now 0.15 mm. from the anterior end of the 
animal; but their essential character has not changed. Figure 23 
(PI. 4 ) represents a parasagittal section of the same embryo of 
which Figure 22 represents a slightly oblique sagittal section. It, 
together with Figure 26,— which represents a cross-section of an 
embryo of the same age, — shows the relation of the i^aired discs to 
the surrounding organs. These discs (else, ee.) are seen to be no 
longer dorsal to the embryonic intestine, as in the previous stages, 
but to have moved to a position in front of it. 
The nervous system has developed considerably. The paired 
nerve-cords (n. v.) have fused with the mid-ventral ectodermic 
ridge, and neuroblasts appear throughout their entire extent. The 
