[74 Embryonic Development of C/iu'onojnus 



Fourth 

 day. 



pletioii, closing-in being facilitated by the sliortening of 

 the body. 



The amnion tears across the ventral surface, and is 

 retracted towards the middle of the back, where its 

 remains continue for a time to be visible on the surface 

 of the yolk. 



In the course of the fourth day all the parts rapidly 

 advance. The wall of the mid-gut is completed. The 



Tracheal 

 system, 



Fig. 128. — Late embryo in egg. i, side view. 2, ventral view. 



envelopes of the reproductive bodies appear. The tho- 

 racic and abdominal limbs become quite plain. Eye- 

 spots appear. The body enlarges in proportion to the 

 head, and its dorsal wall is completed (fig. 128). 



Chironomus is not well suited for the examination of 

 the development of the tracheal system, which is quite 

 rudimentary even in the fully formed larva of the tube- 

 inhabiting species. 



