44 FRANK R. LILLIE. 



such rudiments are formed, although the embryos are very much 

 alike in every other way. It would be interesting to compare an 

 embryo with six post-brachial somites, but I have none yet. 



The central nervous system ends bluntly, except for a short 

 prolongation of the ventral angle of the canal (Fig. 5,^). This 

 condition, which is characteristic for all embryos defective at the 

 hind-end, appears to be due to growth of fibers in the ventral 

 motor zone, for a bunch of neurites extends back on each side of 

 the ventral middle line nearly to the hind end of the notochord. 

 The notochord extends backwards to the extreme posterior end, 

 thus some distance further than the spinal cord. It thus appears, 

 as in the other embryos of this class, to have undergone some 

 regeneration, or at least growth, at the hind end. 



T/ie intestine opens at the posterior end, and is continued as a 

 flat strip along the surface of the splanchnopleure. It is interest- 

 ing to note that this strip has the same histological structure as 

 the walls of the tube proper, showing that the histogenesis 

 depends upon the character of the cells, and not upon such 

 external factors as the form of the tube. The liver is normal. 

 There is no trace of the allantois ; but the stem of the umbilical 

 veins may be seen, in a very rudimentary condition, running in 

 the septum transvcrsum to enter the anterior face of the liver 

 (Fig. 5, B). 



The Wolffian bodies are well developed, and the Wolffian duct 

 much enlarged as in other anallantoic embryos (Fig. 5). Meta- 

 nephric outgrowths are absent. 



Summing up, we may say, that all the embryonic rudiments 

 present have differentiated in the normal fashion. There has 

 been no modification of the numerical value of the somites, no 

 compensating growth, and no regeneration, unless we except the 

 elongation of the notochord. Those embryonic organs, whose 

 rudiment or ordinary locality was destroyed, are simply missing. 



Experiment /./. 



A large part of the hind end was destroyed at the stage of 

 about 52 hours (see operation diagram). The egg was reopened 

 about 68 hours after the operation. The vascular area covered 

 fully half of the yolk ; the heart-beat was vigorous. 



