No. 2.] FORMATION OF THE FISH EMBRYO. 443 



The most successful results were obtained by adding fresh 

 water (from a well) to the sea-water. When put into a solu- 

 tion containing 50 parts of sea-water and 25 parts of fresh 

 water, many embryos developed normally, others showed that 

 the closure of the blastopore was delayed, and several abnormal 

 forms were obtained. The best results were from a mixture of 

 half fresh water and half sea-water. The development of 

 many of the embryos was altered, and generally in a peculiar 

 way. Most of the eggs were killed however by the solution. 

 Eggs put into this solution at the 64-cell stage were dead after 

 24"hours. Other eggs were put into the same solution when 

 the germ-ring had just appeared. Very few formed normal 

 embryos. Many died. Several formed abnormalities. Some 

 of these abnormal forms are shown in the following drawings. 



One very common modification is shown in Figs. 31 and 32. 

 These figures show that the solution has retarded very much 

 the elongation of the embryo posteriorly, but it has not corre- 

 spondingly affected the overgrowth of the germ-ring. Both 

 figures are from hardened embryos at a time when the yolk is 

 still exposed {y) to a small extent. When, finally, the germ- 

 ring closes, the embryo is much shorter than the normal, and 

 much broader. Both the figures show that the embryo is 

 much broader than any stage of the normal embryo. The 

 central plate that should form the nervous system and noto- 

 chord is very much flattened out, and the periphery of this 

 plate is bordered by a zone of tissue which is directly con- 

 tinuous into the germ-ring. 



Cross-sections made through this embryo (Fig. 41) show that 

 the o-erm-ring is directly continuous into the ring around the 

 embryo, and that the quantity and quality of the material 

 seems to be the same in each in cross-section. The border, or 

 ring of the embryo, is composed largely of mesodermal tissue 

 continuous with the lower layer of the germ-ring, and one can- 

 not but draw the conclusion that the material is the same in 

 each. 



The central plate of the embryo is found to be composed of 

 rounded cells, loosely held together, and the plate is vertically 

 much thinner than the border zone of mesoderm. The tissue 



