58 



THE CLASS OF INSECTS. 



tion of the head into the rudiments of the antennary ring, and 

 the supraclypeal piece, and clypeus, together with the approx- 

 imation of the second pair of maxillae, which, when united, form 

 the labium, the extremities of which are now situated in the 

 middle of the body. r<a 



The antennae now extend to the middle of the labium, just 

 passing beyond the extremities of the mandibles and maxillae. 

 The oesophagus can also be seen going from the mouth-opening 

 situated just beneath the labium. It curves around just behind 

 the eyes. There are at this period no appearances of movable 

 blood-disks or of a dorsal vessel. 



The abdomen is now pointed at the extremity and divided 

 into the rudiments of the two anal stylets, which form large, 

 acute tubercles. The yolk-mass is also almost 

 entirely inclosed within the body walls, form- 

 ing an oval mass. 



Another embryo, observed July 27th, had 

 reached about the same stage of growth. The 

 front of the head, including the antennary 

 segment, is farther advanced than before. The 

 entire head is divided into two very distinct 

 regions ; i. e. one before the mouth-opening 

 (the preoral region, including the antennary, 

 or first segment of the head, carrying the 

 organs of vision ; namely, the ocelli and com- 

 pound eyes, and the organs of sense, or an- 

 tennae) ; and the other behind the mouth 

 (pastoral) consisting of the mandibular, or 

 second segment, the first maxillary, or third segment, and the 

 second maxillary, or labial, being the fourth and last segment. 

 At a later period the embryo is quite fully formed, and is 

 about ready to leave the egg. The three regions of the body 

 are now distinct. The articulations of the tergum are present, 

 the yolk-mass being completely inclosed by the tergal walls. 



FIG. 61. The embryo taken from the egg, but nearly ready to hatch. T, the 

 dotted line crosses the main trachea, going through the yolk-mass, now restricted 

 to the thoracic region. At x, the tracheae send off numerous branches around an 

 enlargement of the intestine (colon), where the blood is aerated ; better seen in fig. 

 62. The abdomen consists of eleven segments, the last being a minute triangular 

 piece. 



Fig. 61. 



