. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . Fig. 82.—Diagram of an embryo showing the relations of the vascular allantois to thevilli of the chorion (Cadiat). e, embryo lying in the cavity of the amnion; y$,yelk-sac; al, allantois; , allantoic vessels dipping into the villi of the chorion;ch. chorion. -\-aro. In the mare especially these parts can be readily distin-guished. From the connection of the portion that ultimatelyforms the bladder with themain sac, as indicatedabove, there is ground forregarding the allantoicfluid i
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . Fig. 82.—Diagram of an embryo showing the relations of the vascular allantois to thevilli of the chorion (Cadiat). e, embryo lying in the cavity of the amnion; y$,yelk-sac; al, allantois; , allantoic vessels dipping into the villi of the chorion;ch. chorion. -\-aro. In the mare especially these parts can be readily distin-guished. From the connection of the portion that ultimatelyforms the bladder with themain sac, as indicatedabove, there is ground forregarding the allantoicfluid in the later stages ofgestation, at all events, asa sort of urine. This fluid is at an ear-ly period abundant andcolorless, later yellowish,and finally brown. Sinceat one time it containsalbumen and sugar, itmay serve some purposein the nutrition of thefoetus. When most suggestiveof urine in the latest stagesof gestation, it contains6. Fig. 83.—Diagram of the foetal membranes ofthe Virginian opossum (Haddon, after Os-born). Two villi are shown greatly processes of the cells, which have beenexaggerated, doubtless correspond to thepseudopodia described by Caldwell, al,allantois; am, amnion: , sinus termi-nalis; <«.z, subzonal membrane; r. villi onthe subzonal membrane in the region ofthe yelk-sac; ijs. yelk-sac. The vascularsplanchuopleure (hypoblast and mesoblast)is indicated by the black line. 82 COMPARATIVE PHYSIOLOGY. a characteristic body, allantoin, related to uric acid, urea,etc. Certain bodies, being probably inspissated allantoic fluid,have been termed hippomanes. They may either float freein the fluid or be attached to the allantois by a slender pedicle. The relation of the parts described above will become clearerafter a study of the accompanying cuts and those of precedingpages, in which the allantois is figured.
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