. Journal of morphology. motion observed was performed by an embryo that com-pleted a rotation in just two minutes. The functional value of the ciliary motion is at least two-fold:(1) it bathes the surface of the embryo with currents of waterwhich are subservient to respiration; and (2) rotation of the JOURNAL OF MORPHOLOOy, VOL. 23, NO. 3 522 BERTRAM G. SMITH embryo, when it occurs, serves to prevent adhesion of the embryoto the envelope with consequent abnormahties. The cihation and rotation of the frog embryo have beendescribed by various writers, notably Assheton (96). Piersol(09) has desc
. Journal of morphology. motion observed was performed by an embryo that com-pleted a rotation in just two minutes. The functional value of the ciliary motion is at least two-fold:(1) it bathes the surface of the embryo with currents of waterwhich are subservient to respiration; and (2) rotation of the JOURNAL OF MORPHOLOOy, VOL. 23, NO. 3 522 BERTRAM G. SMITH embryo, when it occurs, serves to prevent adhesion of the embryoto the envelope with consequent abnormahties. The cihation and rotation of the frog embryo have beendescribed by various writers, notably Assheton (96). Piersol(09) has described rotation in the embryo of Plethodon. Stage 19: {jigs. 190 and 21^5 to 248). This stage begins abouttwenty-four hours later than Stage 18. It is characterized byfrom two to three distinct gill invaginations, a budding tail, avery marked outward expression of the pronephros (see especiallyfigs. 245 and 246), and beginning lateral vascular bands, theanlage of the vitelline veins (see especially fig. 245). In addition. 190 191 Fig. 100 Diagram of an embryo of Cryptobranchus allegheniensis in Stage19, showing the direction of the water currents produced by 191 Same as figure 190, for Stage 21. to the cephalic flexure there is a slight cervical flexure whichreaches its maximum in this stage. About sixteen to twentymesoblastic somites are apparent in surface views. In the living embryo, the lateral vascular bands are conspicuousstructures, for they are pink with blood; but they are not yetdifferentiated into true veins. Overlying the upper j^art of theyolk sac, they extend from the heart region longitudinally oneach side of the body and meet posteriorly a little below the this stage and the stages immediately following, theyshift slowly toward the ventral surface. There is considerablevariation in the position of this band in embryos that are otherwisein the same stage. A similar vascular area has been figured forCryptobranchus japonicus by de Lange (07).
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Keywords: ., bookcentury1900, bookdecade1, booksubjectphysiology, bookyear1912
