Plate V. 



Living Embryo* of Oynthia partita; Gastrula to Tadpole. 



Fig. 49. Gastrula showing neural plate, chorda and muscle cells; about 176 cells, 96 ectoderm, 32 



mesoderm, 20 endoderm, 8 chorda, 8 dorsal neural plate and 12 ventral neural plate cells. 

 Figs. 50 and 51. Two stages of one embryo, the second drawn about ten minutes after the first; the 



yellow cells in the mid-line (m'ch.) are mesenchyme cells, the others (ms. ) muscle cells. 

 Fig. 52. Posterior view of elongated gastrula, the blastopore reduced to a narrow slit. 

 Fig. 53. Dorsal view of similar stage, the blastopore a small opening at the posterior end of a groove 

 Fig. 54. An older embryo, the blastopore covered by the forward growth of the posterior lips. 

 Fig. 55. Embryo with inrolling neural plate and with muscle cells arranged in three rows. 

 Fig. 56. Embryo of about the same stage as that shown in figs. 52 and 53; seen from the left side 



showing neural groove, three rows of muscle cells which run transversely to the long 



axis, and a row of mesenchyme cells in the long axis. 

 Fig. 57. Embryo viewed from posterior end, showing blastopore-raphe with open groove above and 



with three rows of muscle cells on each side, also a row of mesenchyme cells. 

 Fig. 58. Young tadpole seen from dorsal side, neural groove open in front and closed behind, small- 

 celled mesenchyme in front of large muscle cells. 

 Fig. 59. Same stage as preceding seen from the right side, showing neural groove, mesenchyme and 



three rows of muscle, cells. 

 Fig. 60. Tadpole of slightly older stage viewed from the posterior (caudal) end showing on each 



side three large muscle cells each of which belongs to a row of such cells (<;/'. tig. 59). 



These muscle cells are connected across the mid-line at the posterior end by a few 



small mesenchyme cells. 



