DEVELOPMENT OF LISSEXCEPHALA. 725 



exterior to it ; neither lungs nor diaphragm have yet appeared; 

 the parallel columns of the neural axis indicate the primary 

 brain-vesicles, by receding from each other in the long cephalic 

 expansion ; a few pairs of protovertebrae show their beginnings 

 at the sides of the myelon, and there is no trace whatever of 

 limbs. The ovum has wholly sunk into a bed of the decidu- 



/ 



ously-developed lining substance of the womb. Before the Mar- 

 supial stage of the foetus has been reached, changes have taken 

 place in the environment of the embryo, and the growth of the 

 abdominal parietes having reduced the wide aperture, shown 

 in fio;. 571, C. to a navel, the embryo with its amnios has 



G v 



sunk into the vitellicle, the trunks of the vitelline artery and 

 veins becoming concomitantly elongated. The allantois comes 

 in contact with that part of the chorion beyond the ( vena ter- 

 minalis,' and, having fulfilled the main purport of its elongation 

 by transporting thereto the allantoic or so-called f umbilical ' 

 vessels, 1 it collapses, and leaves them to their work of organising 

 the fcetal portion of the placenta. The maternal portion is devel- 

 oped upon a whitish area of the inner surface of the uterine horn 

 at the side where the mesometry, fig. 572, g, g, is attached. The 

 gravid uterus of the Rabbit, ten days after pregnancy, presents 

 the appearance given in this figure : the fcetus in its chorion chiefly 

 adheres to the preformed maternal disc at the mesometral side, as 

 shown at d: it is not, however, lodged in a generally expanded 

 segment of the uterine tube, but in a special dilatation thereof, 

 appended, as it were, to the free side of the tube, d, 2 the normal 

 canal of which continues mainly to subserve the lodgment of the 

 placenta. This, in the Rabbit, is an oblong tabulated disc ; 3 I 

 have found it consisting of five lobes or cotyledons : in the Hare 

 it is more compact and subcircular, and about two inches in 

 diameter toward the close of gestation : the inner surface and 

 margins are red, the rest yellowish with red spots, when un- 

 injected: the outer surface is subconcave and uneven, the inner 



1 This is an ambiguous term, applied to different structures which are connected 

 with the navel : e. g. to the vitellicle, as ' umbilical sac;' its A'essels being distinguished 

 by the Greek term for navel. I shall here, as in Vol. II. (p. 263), call the omphalo- 

 mesenteric vessels 'vitelline' and the umbilical vessels 'allantoic,' in reference to the 

 two primitive bags with which they are respectively connected. 



2 This is characteristic of most multiparous lAssencephala, e. g. Shrew, fig. 389, u ; 

 Eat, xx. vol. v. p. 117, nos. 3-166, 3467 ; Guinea-pig, CCLXII". tab. v. fig. 10, in which 

 the normal canal of the uterus is obliterated by the accumulated deciduous substance: 

 ' Spater, wenn die Flachen und Rander des Schleimhautschwulstes bereits mitein- 

 ander versehmolzen, die Hohle des Uterus mit der sich durch sie hiudurchziehenden 

 Epithelialrohre verschwunden ist.' ib. p. 30. 



3 xx. vol. v. p. 168, no. 3472. 



