2i Proceedings of tke Royal Society of Victoria. 



Stage G. — The primitive streak and primitive groove are 

 formed, and at the close of the stage, the notochord can be 

 seen passing forwards from the anterior end of the primitive 

 streak. 



Stage D. — The neural folds appear ; they ai-e widely 

 separate posteriorly, and between them, below the middle of 

 the neu)'al groove, the notochord is clearly seen. 



Stage E. — The first pair of mesoblastic somites appear. 



Stage F. — Four pairs of mesoblastic somites are present. 



Stage G. — Eight pairs of mesoblastic somites are present. 



Stage H. — Fourteen pairs ot mesoblastic somites are 

 present. This is the last stage in which the long axis of the 

 body of the eml jryo lies in a straight line. 



Stage K. — Eighteen to twenty paii s of mesoblastic somites 

 are present. The body of the embryo is just commencing 

 to be curved at the anterior end. The auditory pits are 

 widely open. 



Stage L. — The first gill-cleft appears. Some twenty-four 

 pairs of mesoblastic somites are present. The auditory pit 

 is widely open. The heart lies to the side of the body, and 

 has the form of a tube curved into an S shape. The 

 amnion has grown backwards over the head, nearly to the 

 level of the gill-cleft and the heart. 



Stage M. — Three gill-clefts are present. The outline of 

 the body becomes more clearly marked at the posterior end. 

 The amnion encloses the whole head and neck region. The 

 eye is prominent, and the choroid fissure large and well 

 marked. 



Stage N. — Four gill-clefts present. The amnion commences 

 to grow forward from the posterior end, and the Wolffian 

 ridge appears on either side. 



Stage 0. — Four gill-clefts present. The amnion almost 

 completely encloses the bod3^ The limbs appear as broad 

 processes of the Wolffian ridge. On the ventral surface, the 

 allantois appears as a somewliat hemisj)herical protuberance 

 at the postierior end, and the tail is formed as a blunt curved 

 process. The alimentary canal is nearly closed in. 



Stage P. — The embryo lies completely on its left side, 

 and is completely enclosed by the amnion. Tlie allantois 

 forms a prominent sac-like structure. The anterior and 

 posterior limbs are prominent blunt protuberances. The 



