50 



Of. 0. SARS. 



[No. h 



inferiorly so as to cover the oral parts and legs, all of which are 

 freely exposed. The opaque greenish yolk has now diminished 

 considerably in volume, forming only a central oblong mass within 

 the body and extended bnt little if at all into the head. 



In the stage representert figs. 4, 5, considerable changes have 

 tåken place, both as to the form of the body and the structure of 

 its appendages, though the embryo still exhibits an appearance 

 very different from that of the adult animal. The body, which 

 measures somewhat more than 1 mm. in length, has now become 

 considerably elongated, and the dorsal curvature, very distinct in 

 the preceding stage, is wholly effaced, the body being nearly 

 straight, or but slightly curved ventrally. The frontal edge of 

 the head juts out inferiorly as a small compressed projection^ 

 representing the rostral part of the adult animal, and within this 

 projection the ocellus (oe) has made its appearance as a distinctly 

 defined triangular body tinged with a light-red pigment. Above 

 the ocellus are seen within the head a pair of very faintly defined 

 semicircular opaque masses (0), indicating the place where the 

 compound eye will develop. The pivot-shaped occipital process- 

 ( x) is nearly unchanged, and at some distance behind it, just above 

 the mandibles, a very slight impression indicates the place where 

 the occipital notch will be formed at a succeding stage. The an- 

 tennulæ (a 1 ) have somewhat increased in size and become slightry 

 dilated at the tip; they still project anteriorly in front of the 

 antennæ. The latter organs (a 2 ) are now more fully devel- 

 oped, the scape having assumed its characteristic elbow-shaped 

 form, and the branches being divided into sev en segments, which, 

 however, are still imperfectly defined, without the slightest trace 

 of spines or setæ. The labrum (L) has increased considerably 

 in size, and is now thrown backward so as to obtect the masti- 

 catory parts of the mandibles inferiorly; at the extremity it 

 shows the first trace of the terminal compressed lamella. Behind 

 the mandible the two pairs of maxillæ (m 1 , m 2 ) are distinctly seen. 

 The remaining part of the body has now become considerably 

 elongated and divided into a number of well-marked segments, 

 the posterior part, including the terminal section of the trunk 



