112 FRANKLIN P. REAGAN 



6. Transplanted meroplasts 



It has been seen from Stockard's work and my own that 

 chemical treatment will often produce embryos, the anterior and 

 ventral portions of whose yolk-sacs are practically free from en- 

 dothelium. These embryos may at the same time have a slight 

 dorso-lateral circulation through the ducts of Cuvier and the 

 dorso-lateral yolk-capillaries. A nmnber of such embryos were 

 selected. To the endothelium-free area it was possible in a few 

 cases to transplant an anterior fragment of a normal embryo 

 which had not yet had a circulation. The procedure was as fol- 

 lows: the chorion of the 'host' was partly removed over the en- 

 dothelium-free area. If the rotation of the yolk-sac became 

 troublesome, it was possible to prick the latter in some region 

 where the injury would not be serious. The slight extrusion 

 would hold the embryo in place. A very slight abrasion was 

 sometimes made on the yolk-area where the fragment was to be 

 transplanted. A small receptacle for the tissue was then placed 

 in a wide-mouthed bottle provided with a cork perforated to per- 

 mit the intake and outlet of gases. Oxygen was then generated 

 and allowed to replace the greater quantity of air contained in 

 the bottle; the latter was then sealed. The tissue was moistened 

 from time to time with sea-water which had been boiled and 

 cooled. The oxygen supply was renewed at such times. On 

 the whole the experiment was quite unsatisfactory. The tissue 

 would generally either die or become invaded by endothelium. 



We may consider, however, the most successful attempt which 

 was made. The procedure was similar to that above described. 

 The anterior region, including the otocysts, was transplanted so 

 its ventral surface rested against the exposed yolk-area of 

 the 'host.' The anterior end of the meroplast was directed an- 

 teriorly. The transplanted tissue was badly mutilated, al- 

 though all possible precautions were taken. 



Figure 86 shows a section of the transplanted tissue and its 

 position on the yolk. The morphologically dorsal surface of the 

 tissue lies toward the lower left hand corner of the figure. If 

 the figure be rotated until this corner becomes uppermost, one 



