. La les chordés. Chordés. 88 Structure de base de vertébrés amphibiens donner une preuve que la partie antérieure de l'Miil- lerian conduit est dérivé de structures pronephric, comme cela semble être vrai pour les requins. Dans les reptiles, oiseaux et mammifères, le conduit de Mullerian- velops indépendamment de la Wolff mais très étroitement parallèle à celle-ci (Fig. 87), et il existe des preuves que la région antérieure et de l'ostium conduit Mullériennes surgissent dans de très intime relation avec la pro- nephros. Dans l'ensemble, il semble peu probable que les oviductes sont modifiés deriva- tants de pronephric structures. D

• Contributeur: Library Book Collection / Alamy Banque D'Images
• ID de l’image: RJ51K6
• Taille du fichier: 7,1 MB (347,5 KB Téléchargement compressé)
• Autorisations: Modèle - non | Propriété - non
• Dimensions: 1427 x 1750 px | 24,2 x 29,6 cm | 9,5 x 11,7 inches | 150dpi

Informations supplémentaires

Cette image appartient au domaine public, ce qui signifie que le droit d’auteur a expiré ou que le titulaire du droit d’auteur a renoncé à ses droits. Les frais facturés par Alamy couvrent l’accès à la copie haute résolution de l’image.

Cette image peut avoir des imperfections car il s’agit d’une image historique ou de reportage.

. The chordates. Chordata. 88 Basic Structure of Vertebrates Amphibians give some evidence that the anterior part of the Miil- lerian duct is derived from pronephric structures, as seems to be true for sharks. In reptiles, birds, and mammals, the Mullerian duct de- velops independently of the Wolffian duct but very closely parallel to it (Fig. 87), and there is some evidence that the anterior region and ostium of the Mullerian duct arise in very intimate relation to the pro- nephros. On the whole, it seems somewhat likely that the oviducts are modified deriva- tives of pronephric structures. Differentiation of Sex The vertebrate embryo, during its earlier stages of development, is anatomically in- different as to sex. Every embryo contains the rudiments of all of the urinogenital or- gans of both sexes. As the gonads, in later stages, acquire their definitive differentiation as ovaries or testes, the embryonic parts appropriate to the sex indicated by the gonad likewise proceed to acquire complete and functional differentiation. But the em- bryonic rudiments corresponding to the other sex either cease developing and gradually dwindle away or, at most, progress only to the point of becoming relatively small and imperfectly developed parts having little. Fig. 87. Transverse sec- tion through the urinogeni- tal region of a four-day chick embryo, (g) Mesoder- mal epithelium (perito- neum ) of genital ridge; (m) infolding of peritoneum to form Miillerian duct; (ms) mesentery; (s) mesen- chyme cells which give rise to the stroma (nongenital tissue) of gonad; {t) meso- nephric tubules; (w) Wolf- fian duct. (After Waldeyer. Courtesy, Kingsley: " Com- parative Anatomy of Verte- brates, " Philadelphia, The Blakiston Company.) or no functional significance. Adult males usually possess vestiges of the Mullerian ducts, and adult females hav- ing the metanephros may possess vestiges of mesonephric structures.. Please note that these images are extracted from scanned page

Recherche dans la banque de photos par tags

• bookcentury1900
• collection de livres