114 
Psyche 
[December 
veloped in the embryo and everted upon eclosion. The only 
external indication of wing buds in the first instar is a small 
flange where the pleurum and the tergum join. This flange 
can well be regarded as a lateral expansion of the tergum. 
Hypodermal cells on the tergal portion of the thoracic expan- 
sion grade from pavement epithelium to tall columnar cells, 
as one proceeds laterally. Lacunae are not yet developed, nor 
are tracheae associated with the anlage. 
Second Instar 
Head width .54 mm. Two specimens of this stage were 
studied: one, in the inter-moult phase; the other, just prior 
to its moult to the third instar. In the inter-moult specimen 
both meso- and metathoracic analgen have attained the same 
degree of development. A well marked sinusoid runs along 
the outer margin of each wing expansion, and is incomplete 
in that it does not communicate with the haemoccele either 
anteriorly or posteriorly. In the left rear wing the sinusoid 
is 9[x in length and is occluded in one place by hypodermal 
cells suspended in it. In the other metathoracic expansion 
the sinusoid is evidenced by 20ji and 30p. lengths, separated 
by an occlusion. 
Histological examination shows the sinusoid to be the re- 
sult of attenuated cell ends not going directly to the basement 
membrane of the hypodermis. Instead the processes merge 
with the ends of neighboring cells to leave a space. Precisely 
the same sort of sinusoid is found in the prothoracic expan- 
sion. It follows, therefore, that the sinusoid is not the costal 
lacuna. It may be termed the precostal sinusoid, for it occurs 
peripherad of costa in all nymphal stages. It is a false la- 
cuna situated at the base of large bristles and may be the 
site of trichogen cells. In nymphs about to moult the pre- 
costal sinusoid is obliterated by large trichogen cells. 
Prior to the second moult the costal lacuna is developed. 
It is a space between the basement membrane of the wing 
epithelia and is readily distinguishable from the precostal 
sinusoid which is an intercellular space. In the late second 
instar costa is a marginal lacuna which communicates an- 
teriorly and posteriorly with the hsemocoele. Although a few 
blood cells are present in the posterior portion of the lacuna 
it is not certain that blood can circulate because the anterior 
