MORPHOLOGICAL VALUE OF THE GERMINAL LAMINA. 537 



most simple section, however, shows that the chorda takes up 

 the entire thickness of the middle germinal lamina ; being in 

 contact above with the central nervous system, and below with 

 the glandular lamina. The vertebrae are differentiated in a 

 paired manner from those portions of the germinal lamina 

 that bound the chorda laterally ; and again, the most element- 

 ary sections show that these vertebrae, as Remak long ago 

 demonstrated, undergo subdivision. A portion only of each 

 prae vertebra is converted into bone ; a part certainly becomes 

 muscle, and it may be presumed that a third part becomes the 

 rudiment of the periosteum. 



I have further demonstrated* that at the point where the 

 anterior segment of the cranium subsequently appears, bones 

 and muscles are developed by the formation of boundary or 

 limiting lines in an originally homogeneous material, and no 

 doubt can therefore exist respecting the genesis of the connec- 

 tive-tissue substances. 



Reichert, as has already been stated, first recognized the 

 splitting of the middle germinal lamina for the formation of 

 the pleural and peritoneal cavities. There is no great diffi- 

 culty in demonstrating this fact by the means now adopted 

 for displaying the development of the embryo; namely, by 

 sections. 



It may be seen that the lateral portions bounding the ver- 

 tebrae (lateral laminae, Seitenplatten, Remak) split just as 

 Remak has stated, and become bilaminated, and that the serous 

 cavities develop between them. The walls of these cavities 

 are thus indubitably formed from the middle germinal lamina. 

 For the rest I must refer to the clear description given by 

 Remak, according to whom the upper of these two laminae 

 applies itself to the conjoined nervous and horny lamina, and 

 the lower to the glandular lamina, in order to form on the one 

 hand the body wall, and on the other the intestinal tube. In 

 the former case the horny lamina furnishes the external cel- 

 lular investment and the cellular investment of the superficial 

 glands, but in the latter case the intestinal glandular lamina 

 forms the cellular investment of the cavity of the intestines, as 



* Reichert and Dubois-Reymond's ArcMv, 1864. 



