. Journal of morphology. The ciliary currentsare alike on the two sides of the body. Stage 20: {figs. 192 and 2/^9 to 251). This stage is reachedabout two days later than the beginning of Stage 19. Throughthe loss of the cervical flexure the head is now brought more nearlyin line with the body, but on the other hand there is an increaseill the cephalic flexure. Five gill invaginations are usually visible,the two posterior ones being sometimes indistinct. There aredistinct nasal pits. The roof of the medulla is becoming thin andtransparent. From twenty-five to thirty mesoblastic somitesare appa
. Journal of morphology. The ciliary currentsare alike on the two sides of the body. Stage 20: {figs. 192 and 2/^9 to 251). This stage is reachedabout two days later than the beginning of Stage 19. Throughthe loss of the cervical flexure the head is now brought more nearlyin line with the body, but on the other hand there is an increaseill the cephalic flexure. Five gill invaginations are usually visible,the two posterior ones being sometimes indistinct. There aredistinct nasal pits. The roof of the medulla is becoming thin andtransparent. From twenty-five to thirty mesoblastic somitesare apparent in surface views. The tail undergoes a decidedincrease in size, and is slightly flexed ventrally. The front limbanlagen appear during the latter part of this stage. The lateral vascular bands are not yet differentiated into veins,but during the latter part of this stage some small veins havebeen observed, in living material, extending vertically from thevascular bands for a short distance above them (fig. 192). No. 195 197 Fip;s. 192 to 197 Dcvelopmont of tlic vitelline veins of Cryptobranchus alio-gheuicnsis. All the figures are from living material and, with the exception ofthe veins in figure 192, are drawn with the aid of a camera. X 5. Fig. 192 Stage 20. The stippled area indicates the lateral vascular right and left sides of the embryo are practically alike. Figs. 193 and 194 Right and left views of an embryo in Stage 22. Fig. 195 Lateral, slightly ventral, view of an embryo nearly ready to hatch. Fig. 196 Ventral view of an embryo nearly ready to hatch. Fig. 197 Ventral view of a larva about ten days after hatching. 524 EMBRYOLOGY OF CRYPTOBRANCHUS 525 movement of the blood has been observed in this stage. Theembryos are ciliated, and undergo rotation, much as in the pre-ceding stage. Muscular movements do not ordinarily occur,but have been observed when the embryos were placed in fixingfluids. Stage 21: (figs. 191 and 252 to 255). This stage is reachedabou
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