222 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



heart is formed, develop on the labial to the tenth abdominal segments, 

 inclusive. 



The coelomic sacs of the third to the sixth abdominal segments are 

 formed as in the thorax, but their shape is influenced by the presence of the 



sex-cell mass (Fig. 136£'). 



The germ or sex cells appear early as a 

 wedge-shaped cellular mass at the pos- 

 terior end of the embryonic rudiment at 

 the time of the formation of the inner 

 layer. When the body is fully segmented, 

 the strand of sex cells lies dorsad in con- 

 tact with the visceral wall of the third to 

 the sixth coelomic sacs. Later the second 

 and seventh sacs are also involved. 

 Finally the sex-cell strands become sur- 

 rounded by the compressed part of the 

 coelomic sacs in segments three to six to 

 form a two-layered envelope, the future 

 gonad. The ducts of the gonad form in 

 the posterior segments as in Forficula. 

 The normal incubation period of Carausius 

 morosus is five months,, and development 

 is parthenogenetic. 



CAELIFERA 



The African Migratory Locust 

 (Locusta migratoria migratorioides R. F.) 

 Maturation stages of L. migratoria were 

 not studied by Roonwal (1936), but pre- 

 sumably they are similar to those of 

 Melanoplus differentialis. In the latter 

 species, the eggs, when ready to be laid, 

 all are in the metaphase of the first matura- 

 tion division. The first polar body some- 

 times divides, but whether or not it always 

 does so has not been determined. The second polar body is given off 

 within five to seven hours after being laid. In M. differentialis the 

 maturation divisions occur in the peripheral portion of the yolk and are 

 usually to be found between 0.4 and 0.8 mm. from the micropyle end of 

 the yolk mass. 



The earliest cleavage stage of Locusta studied by Roonwal (1936) was 

 the four-cell stage which occurs about 53^ hours after the egg is laid. The 

 cleavage cells, large stellate masses with well-defined central nuclei, lie 

 close to the posterior end of the egg though distinctly away from the 



Fig. 137. — Locusta. Longitudi- 

 nal section of egg 23 hours old. 

 {cc) Cleavage cells, {yc) Primary 

 yolk cells. 



