240 CHARLES R. STOCK ARD 



fined technique we could get not only embryos otherwise normal, 

 but without ej^es, without normal brain hemispheres, without 

 normal mouth and branchial structures, and without ears, as can 

 now be done, but also simply without a liver, without a pancreas, 

 etc. 



In many of the arrested embryos it would seem highly probable 

 that the total number of red blood-cells in the yolk-sac and body 

 was greatly reduced. The red cells may be considered as a diffuse 

 organ, and this organ seems at times reduced in size as a result 

 of arrest. It cannot be positively stated that the entire embryo 

 in such cases is not proportionately reduced. Thus the proba- 

 bility of having specifically arrested the early blood formation is 

 still questionable. 



The development of one other organ, however, may be fre- 

 quently interfered with by arresting the rate of development of 

 Fundulus embryos for a time immediately following the early 

 embryonic-shield formation. Specimens so arrested by low tem- 

 peratures, treatment with alcohol solutions (Stockard, '10), or by 

 reduced oxygen supply, often show various abnormal condi- 

 tions in the development of the otic vesicle. The vesicle on one 

 side may be absent and the other normal or poorly formed. Or 

 the semicircular canals may not arise and only the ampullae or 

 small cysts may represent the entire ear. 



In such cases, as I pointed out and illustrated in 1910, the 

 cartilaginous capsule representing the hard parts of the inner ear 

 forms immediately around and exactly fits the defective mem- 

 branous arrangement. The cartilage development would seem 

 to be regulated by the membranous portion of the ear. The 

 details of these experiments may be more fully presented when 

 a larger number of these critical moments in organ origin are 

 more exactlj^ located by a further refinement of the experimental 

 method. 



It is most difficult to apply a treatment that is not permanently 

 injurious in such a way as to have the rate of development very 

 low at a given brief interval of time and again restored to the 

 normal rate shortly following. The crudeness of the experiment 

 necessitates bringing on the arrest some time before the particu- 



