530 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. 



elements fall down upon the floor of the cavity, and in order 

 to penetrate between the superior and inferior laminae must 

 necessarily undergo an active or passive migration. 



In both cases the more slowly cleaving large elements form 

 the rudiments of the middle and gland laminae, and modifications 

 only occur in the mode in which this end is attained. In the 

 case of the Fowl, we know that the middle lamina is not com- 

 pleted with the first rudiment of the embryo. I shall hereafter 

 show that in the course of the second day of development a 

 second migration of large coarsely granular elements occurs for 

 the purpose of forming a rudiment of the vessels, the store of 

 which on the floor of the germ cavity, as I may just state in 

 passing, is not exhausted by the first migration. 



In the ova of Batrachia no analogue of the rudiment of the 

 blood- vascular system completing the formation of the meso- 

 blast is discoverable. This, however, may perhaps be referrible 

 to the fact that nothing is at present known in regard to the 

 origin of the bloodvessels in the ova of these animals. In the 

 eggs of Batrachia, also, after the appearance of the rudiment of 

 the mesoblast, a store of large cleavage elements remains behind 

 (fig. 402), respecting the destination of which we know nothing. 



(c.) GERM OF THE FORELLA (TROUT). For the purpose of com- 

 parison, I shall here briefly give the facts that have been 

 acquired in regard to the embryonal laminae in osseous Fishes. 

 Rynek* has studied this subject under my inspection in the ova 

 of the Forella, and his are the only researches which give the 

 results of transverse sections. These show that the segmented 

 germf lies originally in contact throughout its whole extent 

 with the yolk, but that during the expansion of the germ the 

 cavity already known through Lereboullet J is developed. This 

 cavity is completely analogous with the germ cavity of the 

 Fowl's egg. The germ is stretched over the cavity, and rests 

 with a thickened border upon the yolk at the margin of the 

 cavity. The part stretched over the cavity exhibits again, in 



* Max Schultze's Archiv, Band v. 



t The cleavage was first described by Rusconi in Mliller's Archiv for 

 the year 1836. 



I Noui-elks Eecherches et Annales des Science Nat. Zoologie, Tom. ii., 1864. 



