No. 2.] BLATTA AND DORYPHORA. 369 
short, chitinous cylinder, projecting somewhat from the general 
surface of the segment. Its inner walls are lined with spines 
which are directed outward. The abdominal spiracles, though 
smaller, are also lined with similar spines (Fig. 85 ¢v). The first 
pair of tracheze send large branches to the head. The abdominal 
trachez of each side of the body anastomose to form a longi- 
tudinal trunk, from which the branches ramify to the different 
organs. The invaginated ectodern, at first very thick (Fig. 84 
tr), gradually thins out as the respiratory tubes lengthen and 
ramify. The thin epithelium thus formed secretes the chitinous 
lining provided at the time of hatching with the spiral thicken- 
ings so characteristic of insect trachez. 
The proctodzum and stomodzum when first formed are tri- 
angular in cross-section. Later both become hexagonal (Figs. 
79 and 80). A like pronounced similarity in form between the 
stomodzeum and proctodzum of Gammarus has been observed 
by Pereyaslawzewa (40). She says: ‘Fait tres intéressant, qui 
mérite d’étre noté, c’est qu’a mesure de l’acroissement du rectum 
et de l’cesophage, leur partie intérieure affecte absolument la 
-méme forme carrée, dont les parois sont concaves. Ce qui 
concerne la configuration des cavités, elles n’en différent aucune- 
ment et se dessinent sous forme d’une croix oblique; la dis- 
semblance consiste en ce que dans Vcesophange ce sont les 
parois qui s’enfoncent, tandis que les parois du rectum sont 
tapissés d’un epithelium cylindrique, dont les cellules s’aplatis- 
sent graduellement vers les angles.” 
The three pairs of Malpighian vessels appear at a very early 
period, while the proctodzeal invagination is still very shallow. 
They are from the first hollow diverticula, and have their blind 
ends pushed back by the forward growth of the proctodzum. 
Thus it happens that a transverse section through the tail-end 
of an embryo in the stage of Fig. 74 passes through both the 
proctodzeum and the Malpighian vessels (Fig. 79, 7, mpg, mpg). 
When the blind ends of the six tubes have struck the body wall, 
their continued growth forces them to turn and grow forward. 
After the formation of the dorsal body wall, they may be found 
lying as thin undulating tubes, surrounding the mesenteron at 
approximately equal distances from one another (Fig. 86 mg). 
The very early appearance of the Malpighian vessels and 
their paired arrangement in Doryphora, Fig. 72, would seem to 
