182 



INTERNAL FACTORS 



IV. i 



tulae with closed blastocoel and these to normal Planula larvae. 

 In Clytia a hydroid was eventually reared and in Liriope a 

 medusa with four primary tentacles from \ and \ cells. It is to 

 be noticed that, since the third division in these eggs is equatorial, 

 the | and ^ blastomeres must be either animal or vegetative. 



Zoja also finds that in Laodice and Clytia the number of cells 

 in partial larvae is proportional to the germinal value. In 

 Liriope the number of cells in the endoderm is equal to that 

 in the whole (4-) larva. 



FIG. 91. 



Partial development 

 in Coelenterata. 

 (After Zoja, 1896.) 

 a-d. Laodice cruci- 

 ata : a, f blastomeres : 

 b, blastomeres ; c, 

 blastula from \ blasto- 

 mere; d,^ larva during 

 formation of endo- 

 derm. e-l. Liriope tnu- 

 cronata. e-i. Develop- 

 ment of | blastomere : 

 e, division of i blasto- 

 mere into f ; /, | ; g, 

 fg ; h, end of endoderm 

 formation in ^ em- 

 bryo ; i, medusa reared 

 from ^ blastomere. 

 j-l. Development of j 

 blastomere : j, f ; k, 

 j^; 7, embryo with 

 endoderm. 



LITERATURE 



E. METSCHNIKOFF. Ernbryologische Studien au Medusen, Wien, 1886. 

 R. ZOJA. Sullo sviluppo dei blastomeri isolati dalle uova di alcune 

 meduse, Arch. Ent. Mech. i, ii, 1895-6. 



