EMBRYONIC DEVELOPMENT OF THE MANTID 225 



During this time the posterior and lateral margins of the germ 

 band undergo a folding which initiates the growth of the embry- 

 onic envelopes. This fold extends laterally forward along the 

 edges of the germ band, and extension toward the midline of 

 the germ band proceeds until the edges unite, forming the 

 amnion and serosa. 



Further development consists in the enlarging and rounding 

 of the cephalic lobes, accompanied bj^ a continuation of growth 

 at the posterior end of the germ band. The region immediately 

 caudal to the lobes retains its width, while after the embryonic 

 rudiment has attained a length of about 0.6 mm. to 0.7 mm., 

 extension posteriorly is apparently retarded slightly, and a 

 lateral development of the posterior third of the germ band 

 takes place. This area becomes a little wider than the middle 

 third. In this sequence of growth we find three distinct de- 

 \'elopments; first, a marking off of an anterior third of the germ 

 band which will subsequently give rise to the eyes, brain, anten- 

 nae, etc.; second, a middle third from which the mouthparts 

 apparently arise; third, a posterior part destined to become the 

 thoracic region and from which the thoracic appendages are 

 later developed. While three quite distinct regions may be 

 observed, they cannot be considered as macrosomites in any 

 sense, for they are identified by minor external conformations 

 only and are not separated by any process of segmentation. The 

 posterior termination of the thoracic region consists of a rounded 

 area of cells whose activity will be discussed presently. 



During the development just described the embryonic rudi- 

 ment has lengthened from about 0.65 mm. to a little over 0.9 

 mm. Up to this point the entire area has revealed no differentia- 

 tion in structure; there is what appears in external view simply 

 as a peculiarly shaped homogeneous mass of cells. 



The indusium. A peculiar serosal structure has been observed 

 in this and in several succeeding stages which resembles very 

 closely an early stage of the indusium of Xiphidium with which 

 I think it should be homologized. According to Wheeler ('93) 

 the indusium of Xiphidium becomes a large three-layered organ 

 enveloping practically the entire egg. Subsequent study has 



JOURNAL OF MORPHOI-OGY, VCL. 30, NO. 1 



