DEVELOPMENT OF PEEIPATUS NOV^-ZEALANDI^. 257 



the dorsal side of the anus. The central yolk mass is much 

 reduced in bulk. The somatic wall of the somites is much 

 thickened, and in the anterior segments pushes out the ecto- 

 derm covering it, so as to form the leg portion of the somite ; 

 a small ventral outgrowth represents the rudiment of the 

 nephridial duct. The ectoderm over the leg ridges is thickened, 

 and at the internal ventral angles of this thickening there are 

 special rounded elements which are the origin of the nerve- 

 cords. The cerebral lobes of the nervous system are joined 

 together in front of the mouth by a cerebral commissure. 



In conclusion, I wish to express my thanks to Mr. Sedgwick 

 for his kindness in providing me with my material, and for the 

 assistance which he has given me throughout my work. 



