58 



dorsal direction appears as a narrow oblong with its greatest length 

 extending transversely to the long axis of the embryo. This is the 

 fundament of the labrum. On each side of the labrum is a wide 

 lobe-like thickening of the ectoderm, the two constituting the pro- 

 cephalic lobes, and on each side of these is a small knob-like thicken- 

 ing, representing the antennae. The antennae are not so well-devel- 

 oped as in Myrniica (see PI. VIII, Fig. 33). The fundaments of 

 the antennae were noted by Ganin ('69), but he did not know what 

 they represented. He says : "Es muss hier noch bemerkt werden dass 

 man in solchen Entwicklungs-stadium auf den Seitentheilen jedes 

 Kopflappens ein besonders rundliches Hockerchen beobachten kann ; 

 iibrigens existiren diese Hockerchen nur kurze Zeit und haben keine 

 definitive Bedeutung; in den spateren Entwicklungsstadien kann man 

 sie nicht mehr unterscheiden." Wheeler (1910, p. 72) mentions the 

 presence of traces of the antennae in the embryo of Formica gnava. 



Back of the stomodaeum occur three pairs of lobe-like evagina- 

 tions, the fundaments of the mandibles, maxillae, and labium re- 

 spectively. On the three following segments occur three similar lobe- 

 like thickenings which are somewhat smaller than those representing 

 the mouth parts. These represent the three pairs of thoracic legs. 

 Back of the thoracic segments occur ten other segments, upon which 

 occur very small paired tubercles representing abdominal append- 

 ages. On each side of the second thoracic segment occurs an irregular 

 slit-like opening, the first thoracic spiracle. A pair of such openings oc- 

 curs on the last thoracic seginent and one on each of the following 

 ten abdominal segments. Figure 23, Plate VI, represents a slightly 

 older stage than Figure 22, Plate V. The dorsal part of the em- 

 bryo has been removed, the yolk taken away, and the ventral part of 

 the embryo straightened out to show all the segments. This corre- 

 sponds to the stage of Formica gnava figured by Wheeler (1910, 

 pp. 69). At this stage the ventral thickening extends almost half- 

 way around to the dorsal side. 



Figure 24 represents a later stage, in which the embryo has 

 straightened, the mouth parts extending directly forward instead of 

 ventral as in Figure 22. The mesenteron is smaller, and shows as 

 a regular oval in the middle of the body. Its ends are in contact 

 with the now more fully developed stomodaeum and proctodaeum, 

 although communication between the two has not yet been estab- 

 lished. The stomodaeum extends backward as a narrow tube, while 

 the proctodaeum is a much shorter, somewhat oval sac. 



The posterior border of the head is indicated by a constriction, 

 but there is no differentiation between thorax and abdomen at this 



