610 DEVELOPMENT OF THE EGG IN HUMAN SPECIES. 



Fig. 214. 



has gone on for some time, the external surface of the chorion pre- 

 sents a uniformly velvety or shaggy appearance, owing to its being 

 covered everywhere with these tufted and compound villosities. 



The villosities themselves, when examined by the microscope, 

 have an exceedingly well-marked and characteristic appearance. 

 (Fig. 214.) They originate from the surface of the chorion by a 



somewhat narrow stem, and divide 

 into a multitude of secondary and 

 tertiary branches, of varying size 

 and figure ; some of them slender 

 and filamentous, others club-shaped, 

 many of them irregularly swollen at 

 various points. All of them termi- 

 nate by rounded extremities, giving 

 to the whole tuft a certain resem- 

 blance to some varieties of sea-weed. 

 The larger trunks and branches of 

 the villosity are seen to contain nu- 

 merous minute nuclei, imbedded in 

 a nearly homogeneous, or finely gra- 

 nular substratum. The smaller ones 

 appear, under a low magnifying 

 power, simply granular in texture. 



These villi are altogether peculiar 

 in appearance, and quite unlike any 

 other structure which may be met with in the body. Whenever we 

 find, in the uterus, any portion of a membrane having villosities 

 like these, we may be sure that pregnancy has existed; for such 

 villosities can only belong to the chorion, and the chorion itself is 

 a part of the foetus. It is developed, as we have seen, as an out- 

 growth from the intestinal canal, and can only exist, accordingly, 

 as a portion of the fecundated egg. The presence of portions of a 

 shaggy chorion is therefore as satisfactory proof of the existence 

 of pregnancy, as if he had found the body of the foetus itself. 



While the villosities which we have just described are in pro- 

 cess of formation, the allantois itself has completed its growth, and 

 has become converted into a permanent chorion. The bloodvessels 

 coming from the allantoic arteries accordingly ramify over the 

 chorion, and supply it with a tolerably abundant vascular network. 

 The growth of the foetus, moreover, at this time, has reached such 

 a state of activity, that it requires to be supplied with nourishment 



Compound villosity of HUMAN CHO- 

 RION, ramified extremity. From a three 

 mouths' foetus. Magnified 30 diameters. 



