Tliini Day 



^73 



a mucli larger proportion to tlie rest of the body than 

 ill the hirva after hatching. The fore-giit and hind-gut 

 are plainly visible, and about this time join the mid-gut, 

 which is still very incomplete, not enclosing the yolk on 

 the dorsal side (fig. 126}. The fore-gut pushes into the 

 mid-gut, which it indents and breaks through. Continuing 

 to lengthen, the fore-gut protrudes for a certain distance, 

 and is then reflected, meeting the wall of the mid-gut 

 ^vitll a marked break in continuity, as fig. 126 shows. 

 It is not true, as has been said by Weismanii and others, 

 that the wall of the cardia (' proventriculus '} is derived 

 from the fore-gut ; it is altogether entodermic, as is 

 evident from a careful ex- 

 amination in any st^ge. 

 The future reproductive 

 organs are represented by 

 two cellular masses Ij'ing 

 in the yolk within the 

 hinder end of the abdomen, 

 which is strongly bent in- 

 wards. The nervous system 

 is a gangliated cord of 

 relatively large size. The 

 serosa completely invests 

 the body. 



During the third day of development the jaws begin Third day. 

 to assume their ultimate form and arrangement. The 

 maxillae of the second pair unite to form a labium. 

 The prothoracic limbs appear, and the first indications of 

 the anal feet may sometimes be made out. The body has 

 now contracted to such a degree that the anus lies at the 

 posterior pole of the egg, the head being bent backwards 

 on the dorsal surface, and resting upon a large mass of 

 yolk. The ento-mesodermal rudiments are fast growing 

 round the yolk, and the dorsal wall approaches com- 



FiG. 127. — Diagram of development 

 of oesophageal valve and cardiac 

 chamber. X 300. 



