BY VERA IRWIN-SMITH. 255 



On the otlier hand, the heart spiracles (?) are relatively much larger 

 and more prominent {sp.). A small area of dark cuticle above each of them, 

 indicates the position in which the lateral "boss" grows out later, evidently as 

 a protective structure above the spiracle. 



On the dorsal surface of each of the body segments there are instead of six, 

 only two stout bristles. Tiny rudiments of the other bristles can be seen on some 

 segments. The smallest larvae collected in the iield, 2 mm. long, show these on 

 all segments (Fig. 7), and the first bristles developed are found to be the middle 

 one on each side. On the ventral surface, six bristles are present in the newly- 

 hatched larva, but they are not equally developed and are very small and incon- 

 spicuous (Fig. 6). The outermost bristle on each side is the longest, and this is 

 the case, still, at the 2 mm. stage (Fig. 8). It is, therefore, only with later growth 

 that all the bristles of each surface become uniform in size. On the lateral 

 ridges only the two larger bristles are present at first. These, at hatching, are 

 about 0.12 mm. long, and give the larva a conspicuously hairy appearance. 



The larva escapes from the egg through an irregular rupture extending up 

 from the broad pole (Fig. 1). The first moult evidently occurs immediately 

 after hatching, since many cast skins were found tangled up with the empty egg- 

 cases (Fig. 1). These skins differ considerably from those of later moults. They 

 are very soft, and delicate, do not retain the shape of the larva, and are not 

 coated with calcareous hexagonal plates. In place of the plates are numerous 

 delicate, finely-pointed processes (Fig. 2) scattered irregularly between the 

 bristles. In larvae still contained in the egg, the armoured coat can be seen, 

 already developed, beneath this skin. The structure of the head can be made 

 out more easily in the moult skin than in the unhatched larva. Both show au 

 earlier stage of development than the hatched larva, which is especially interest- 

 ing in the case of the mouth-parts. These will be considered later, in conjunc- 

 tion with a detailed study of the fully-developed larval mouth-parts. The 

 structures which have the appearance of spiracles are very conspicuous, and each 

 is seen to connect, internally, with a small tube, which can be traced for a 

 short distance into the head. 



