

EMBRYOGENIC METHOD 55 



from the segmentation of the human egg or the 

 form Morula. 



4. A Planead stage, similar to the ciliated larvae 

 of the Invertebrates and of the Amphioxus. 



5. A Gastreada stage, in which the embryo is 

 hollowed out from a cavity like the gastrula of the 

 lower invertebrates. 



6. A stage similar to that of the existing Tur- 

 bellarian worms, that is to say, long in shape and 

 without a general cavity of the body. 



7. A Scolecide stage, differing from the preceding 

 by the presence of a sanguine liquid and of a splanch- 

 nic cavity. 



8. A Sack-worm stage, approaching the existing 

 Tunicates and presenting, like the larvae of the 

 Ascidia, a rudiment of spinal marrow and of back- 

 bone. 



9. An Acranian Vertebrate stage, of which the 

 existing Amphioxus can give us a near idea. 



10. A Monorhinian stage analogous to the lam- 

 prey type, with a rudimentary cranium without 

 jaws. 



11. A Selachian stage, very like the lower dog 

 fishes of the present time ; the division of the nostrils 

 and the apparition of a frame of jaws and of two 

 pairs of limbs differentiate it from the preceding 

 stage. 



12. A Dipneustal stage, the first type of pulmonary 

 respiration marking the first step towards the 

 Amphibians. The present Lepidosiren gives us an 

 approximate idea of this. 



13. A Sozobranch stage, with lungs and persistent 

 gills, as in the existing Axolotl ; this type is 



