376 



FISH FOR EXPERIMENTATION 



were differentiated. Devillers (1947) cultured the small pike egg in 3 times Holtfreter's 

 solution beginning at the blastula stage to secure definitive embryonic structures. The 

 trout egg (Salmo fario) did not give comparable results, indicating ontogenetic stage and 

 differentiation may not be the same in different species. Oppenheimer (1947) believes 

 that the yolk has a physical relationship to the early morphogenetic movements which 

 must not be minimized. 



o' ", 



Representation in the cleaving blasto- 

 derm of the embryonic areas mapped 

 out in the gastrula. The long axis is 

 here represented by the second plane 

 of cleavage. 



The nervous system is indicated by 

 vertical hatching, notochord by heavy 

 stipple, endoderm by light stipple, 

 and mesoderm by horizontal hatching. 



.#.2< 



j^.2.Z 



Ifotochonl and endodara 



Nerrous sjrstom posterior to midbrain 



Mesoderm, midbrain to 2d somite 



Endoderm, mesoderm 



Mesoderm posterior to ?d somite 



Nervous s/stem and mesoderm, forebraln 



Posterior mesoderm 



Mesoderm and extra-smbryonlc membrane 



Hotocbord and endoderm 



nervous system posterior to midbrain 



Mesoderm, midbrain to 2d somite 



Endoderm, mesoderm 



Mesoderm posterior to 2d somite 



Nervous sjstem and msBodem, forebraln 



Posterior mesoderm 



Mesoderm and extre-esbryonl z membrane 



C«r>-rlng -- tall -bud blastema 



Extra- embryonic membrane 



Germ- ring 



Extra-embryonic membrane 



Extra-embryonic membrane 



Germ- ring 



Extra -embryonic membrane 



Cerm-rlng •- tail-bud blastema 



Extra- embryonic membrane 



Cera- ring 



Extra -embryonic membrane 



Extra -embryonic membrane 



Germ- ring 



Extra-embryonic membrai.e 



CELL LINEAGE OF FUNDULUS. SCHEME FOR THE LOCATION OF MATERIALS 

 IN THE BLASTODERM WHEN THE FIRST CLEAVAGE IS TRANSVERSE 



(From Oppenheimer 1936: Jour. Exp. Zool. 73:405) 



The axis of the second cleavage plane tends to coincide with the longitudinal axis of the 

 embryo. Cleavage, in general, tends to be geometric and so predictable that early cell 

 lineage studies are possible. Teleost cleavage is essentially the non-determinate type. 

 There are variations in the qualitative distribution of parts of the blastodisc so that 

 Oppenheimer (1936) says: "This lack of constancy of relationship between particular 

 cells of the cleaving blastoderm and specific parts of the embryo is, of course, strictly 

 compatible with the fact that the development of the teleost is of the inductive type. " 



Pasteels (1936) and Oppenheimer (1936) have shown, by means of vital staining, that the 

 fate map of Salmo and Fundulus are not unlike those for the Amphibia; that the periphery 

 of the blastoderm furnishes the mesoderm for the embryo; that the prospective endoderm 

 is found in the cellular blastoderm rather than in the yolky portion of the egg; that the 

 prospective chorda lies in a crescentic area (Fundulus) just anterior to the prospective 

 endoderm; and that the prospective nervous system lies just anterior to the chorda-meso- 

 derm. Gastrulation does not involve differential mitosis but rather (as in the Amphibia) 

 a re-arrangement of the cells, the types of movement being described as involution, ex- 

 tension, and convergence. The initial expansion of the blastoderm is considered as epi- 

 bolic movement. 



