Text-book of comparative anatomy . Fig. 353, B). These rudiments degenerate later. The origin of the two endodermal cell layers, which we saw appear in thetransverse section (Fig. 350, F), is difficult to explain. At the stage at which thissection is taken, the whole endodermal rudiment consists of two lateral cell streaks. CLf Fig. 352.— A-E, Ventral view of 5 stages in the development of Hydrophilus (after Heider).The anterior end is directed upward, a and b, Points at which the blastopore first closes ; a/, edge ofthe amnion fold; a/, caudal fold; af, paired cephalic fold; an, antenna; es,
Text-book of comparative anatomy . Fig. 353, B). These rudiments degenerate later. The origin of the two endodermal cell layers, which we saw appear in thetransverse section (Fig. 350, F), is difficult to explain. At the stage at which thissection is taken, the whole endodermal rudiment consists of two lateral cell streaks. CLf Fig. 352.— A-E, Ventral view of 5 stages in the development of Hydrophilus (after Heider).The anterior end is directed upward, a and b, Points at which the blastopore first closes ; a/, edge ofthe amnion fold; a/, caudal fold; af, paired cephalic fold; an, antenna; es, terminal segment;g, pit-like invagination (rudiment of the amnion cavity); 7;, procephalic lobes ; r, groove-likemedio-ventral invagination ; s, germ-streak covered by the amnion. between the yolk and the two rows of mesoderm cavities. Anteriorly at thestomodseum and posteriorly at the proctodseum the two streaks pass into oneanother. At earlier stages the endoderm consists of an anterior and a posteriorU-shaped double streak. The limbs of the U, which are very short to begin with,are at first directed backward in the anterior double streak, and forward in theposterior streak ; they gradually elongate till at last the two anterior limbs meet thetwo posterior, and thus give rise to the two above-mentioned endoderma
Size: 2315px × 1080px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
