Jy OP THE "FIGURES. 



XVU 



Fig. \ Fig. 



313, 314 Sections of the egg of a 334 

 mammal ; v, the thick vitelline 

 membrane or chorion ; y, the 

 yolk ; s, the germinative spot ; 

 g, the germinative vesicle ; 

 k, the empty space between 

 the vitelline sphere and cbo- 



non. 



315 Shows the first indication of 

 the germ dividing into layers, 



335 

 336 

 337 



338 



the serous 

 cous (m). 



(s) and the mu- 339 



is seen sur- 



343 

 344, 



346 



347 



348 



316 The mucous layer (m) expands 



over nearly half the yolk, and 

 becomes covered with many j 

 little fringes. 



317 The embryo (c) 



rounded by the amnios (6), and 

 covered by the large allantois 

 (a) ; p, e, fringes of the cho- 

 rion ; /;, m, fringes of the ma- 

 trix 



318 One of the chalazae of a jack- 



pulled straight. 



[\Vagner 



319 "Vitellus of a hen's egg Ibid. 



320 The yolk of a jackdaw's egg. 



[Ibid. 



321 Section of a yolk almost ripe 



included in its calyx . Ibid. 



322 The ovary of a fowl . Ibid. 

 323, 324 The" vitellus twelve hours I 359 



daw's egg 



after incubation 



Ibid. 360 



325 Magnified view of the blasto-[361 

 derma . Ibid. 



326 Ideal sections 



Baer 



327 Yolk after eighteen hours' in- 



\-f 



cubation 



Wagner 



328 The pellucid area magnified. 



[Ibid. 



329 Ideal sections of 327, 328. Ibid. 



330 Yolk after twenty-four hours' 



incubation . . . Ibid. 



331 Magnified view of the pellucid 



area .... Ibid. 



332 Ideal sections of 329331. 



[Ibid. 



333 Yolk of the natural size after 



thirty-six hours' incubation. 



[Ibid. 



Magnified view of the pellucid 

 area of the vitellus Wagner 

 Ideal sections of the embryo. 



[Ibid. 



Incubated vitellus of the jack- 

 daw's egg . . Ibid. 

 Anterior extremity of an em- 

 bryo .... Ibid. 

 Ideal section of an embryo. 



[Ibid. 



342 Views of embryos mag- 

 nified . . . [Ibid. 

 Ideal section of ditto . Ibid. 

 345 Outlines of embryos of the 

 fowl .... Ibid. 

 View of the vitellus magnified. 



[Ibid. 



View of the embryo of the 

 yolk .... Ibid. 

 Yolk of the hen's egg . Ibid. 

 349 354 Views of embryos in dif- 

 ferent stages of development. 



[Ibid. 



355 Embryo of a lizard (Lacerta 



agilis) . . . Ibid. 



356 Vorticella, showing its reproduc- 



tion by buds . Agassiz 



357 Vorticella, showing its repro- 



duction by division . Ibid. 



358 Polyps, showing the same phe- 



nomenon . . . Ibid. 

 A chain of Salpae . Ibid. 



An individual Salpa . Ibid. 

 Cercaria, or early form of the 



Distoma . . Steenstrup 



362 Distoma, with its two suckers. 



[Ibid. 



363 Nurse of the Cercaria . Ibid. 



364 The same magnified, showing 



the included young . Ibid. 



365 Grand nurses of the Cercaria, 



including the young nurses. 



[Ibid. 



366 Stages of development of the 



Acalephae (Mtdusa) : a, the 

 embryo in its first stage, much 

 magnified ; b, summit, show- 

 ing the mouth; c, f, g, ten- 

 tacles shooting forth; e, 

 embryo adhering, and forming 

 6 



