368 WHEELER. [ VoL. III. 
derm near the base of the labrum. Punktsubstanz is formed in 
this ganglion in the same manner as in the brain and ventral 
ganglia. It is ultimately loosened from the stomodzeum, and 
becomes surrounded by mesodermic elements. Later the four 
pairs of ganglia of the intercalary, mandibular, Ist and 2d max- 
illary segments fuse and form the infracesophageal ganglion. 
That the outer neurilemma is of ectodermic and not of meso- 
dermic origin seems to be proved by the fact that shortly after the 
separation of the nerve-chord from the integumentary ectoderm, tt 
sheds from its surface a delicate chitinous cuticle stmultaneously 
with the shedding of the first integumentary cuticle. This cuticle, 
which is separated from the surface of the outer neurilemma, and 
even from the surfaces of the main neural trunks, is afterwards 
absorbed. 
The six ocelli are formed as apple-shaped thickenings of the 
optic plate. Their small size has hindered me from studying 
their structure in detail. I have represented in Fig. 81, soon 
after their first appearance, two of the ocelli corresponding to 
the eyes of Aczlzws numbered V. and VI. by Patten. Each 
forms a slight depression somewhat paler than the surrounding 
ectoderm. The nucleus (7) of one of the central cells is seen 
to be much larger than the nuclei of the surrounding cells. 
Patten has described and figured this same large nucleus in the 
éyes or Actus (Pl. XI., Figs: 63, 64, 65; etc.). 
The five pairs of invaginations anterior to those of the second 
maxillary segment form the tentorium of the larval head. These 
invaginations grow inwards:-as slender tubes, which anastomose 
in some places. Their lumina are ultimately filled with chitin. 
Palmén (36) found that the tentorium of Lphemerids breaks 
across the middle during ecdysis, and that each half is drawn 
out of the head, like the chitinous lining of a tracheal tube. 
This fact, together with my observations on the tentorium of 
Doryphora, makes it highly probable that, as Palmén suggests, 
the tentorium is formed from trachez, which have become 
modified for muscular attachment. 
Of the true tracheal invaginations, those of the pro- and 
meta-thorax disappear. The mesothoracic spiracle comes to lie 
between the pro- and meso-thoracic segments near the base of 
the legs and ventral to the line of abdominal spiracles. This 
first spiracle is the largest, and in cross-section appears as a 
