DEVELOPMENT OP THE CAPE SPECIES OF PER1PATUS. 373 



The Development of the Cape Species of 

 Peripatus. 



PART IV. 



THE CHANGES FROM STAGE G TO BIRTH. 



By 



Adam Sedgwick, M.A., P. U.S.. 



Fellow of Trinity College, Cambridge. 



With Plates XXVI, XXVII, XXVIII, and XXIX. 



The changes which take place during and subsequent to 

 Stage g are mainly changes of growth and histological differ- 

 entiation. The most important organs which have not yet 

 made their appearance by the close of Stage f, are the crural 

 glands and tracheae. The origin of the latter is, I regret to 

 say, still hidden from me. The remaining organs have acquired, 

 in all essential respects, the adult relations by the close of 

 Stage f. 



The Ectoderm. 



In Stage g, the ectoderm retains the characters already 

 described in Part III, p. 472. It forms an extremely thin, 

 much vacuolated layer over the greater part of the body, and 

 the nuclei are far apart and in a single layer (fig. 5). In 

 embryos of this age, the ectoderm does not contract when the 

 embryo is preserved, and no doubt its extreme tenuity is due 

 to this fact. On the ventral organs the ectoderm is thicker 

 and the nuclei in more than one layer and close together. 

 On the dorsal hump also, the ectoderm still remains thick, 

 with a large amount of protoplasm external to the nuclei. 



