GENETICS OF FISH 



401 



The teratological forms of fish embryos produced by irradiating germ cells. No. 1 represents a control 

 embryo 4 days after fertilization. No. 2 shows slight reductions in the anterior and posterior regions. 

 The succeeding stages (3, 4 and 5) show greater reductions of head and tail. Other ports are entirely 

 lacking in these embryos. Deformities of the heart are shown in drawings to the right of each embryo. 

 Embryos deformed as much as No. S often do not develop a heart. The heart deformities consist 

 chiefly of an elongation, and improper formation of the chambers, usually associated with an edema 

 of the pericardial cavity. 



(From Solberg 1938: Jour. Exp. Zool. 28:417) 



DISCUSSION: 



The foregoing sections on Fish indicate that this Class of Vertebrates is coming into its 

 own in the field of Experimental Embryology. Most of the procedures outlined are of an 

 operational nature. 



There are also the studies on hybridization; on environmentally induced teratologies 

 (Stockard, 1921); on the effect of x-irradiation of one of the gametes (Solberg, 1938); on 

 the physiological response of the embryo to changes in the environment (Waterman, 1940 

 and the various Japanese workers with Oryzias). There is an ever increasing amount of 

 work of a cytological and cytochemical nature, all of which should be included in an ex- 

 haustive treatise on experimental embryology of fish. 



The fish are rapidly becoming a contestant for attention along with the ainphibia. Pos- 

 sibly the work of Oppenheimer (1939) can be cited as a bridge between these two classes 

 of vertebrates, for she found that a large variety of fish anlagen differentiated quite nor- 

 mally when grafted into the amphibian hosts and that "Fish epidermis and cartilage have 

 been found morphologically continuous with comparable structures formed by amphibian 

 cells in grafts," and "the fish grafts are occasionally seemingly innervated by nerves 

 originating from the amphibian cranial ganglia; it is not known whether the apparent in- 

 nervation is a functional one. " (Jour. Exp. Zool. 80:392) 



