FIG. 200 



Figs. 200-215. — Development of lamprey, Petrotnyzon planeri. Figs. 200-204, 208-212 

 X 18, others X about 30. 200, 201. First cleavage, beginning and concluded. 202. Third 

 cleavage. 203. Fourth cleavage, in section, showing beginning ot" segmentation cavity. 204, 

 205. Early and late blastulas, in section. 206, 207. Early and late gastrulse, in section. 208, 

 210, 212. Early embryos showing growth of head end. 209, 211. Sagittal sections of early 

 embryos showing differentiation of organs. 213, 214. Transverse sections of early embryos. 

 215. Sagittal section of newly hatched larva, Amniocates. (Figs. 211, 215, after GOETTE, others 

 after V. KUPFFER.) 



BP. Blastopore. C. Ccelenteron. CH. Notochord. DL. Dorsallip of blastopore. EC. 

 Ectoderm. EN. Entoderm. EP. Epiphysis. G. Gut. H. Heart. Af. Central nervous 

 system. MES. Mesoblast. A\ Nasal pit. NC. Neurenteric region. J^". Mouth pit, stomo- 

 daium. SC. Segmentation cavity. T. Thyroid gland. Y. Yolk and yolk cells. 



189 



