EXPLANATION OP THE TTIGUEES. 



xvu 



Fig. 



313, 314 Sections of the egg of a 

 mammal ; v, the thick vitelline 

 membrane or chorion ; y, the 

 yolk ; s, the germinative spot ; 

 ff, the germinative vesicle; 

 A, the empty space between 

 the vitelline sphere and cbo- 



iFig. 



334 Magnified view of the pellucid 



area of the vitellus Wagner 



335 Ideal sections of the embryo. 



[Ibid. 



336 Incubated vitellus of the jack- 



non. 

 315 Shows 



the first indication of 



the germ dividing into layers, 

 the serous (s) and the mu- 

 cous (ni). 



316 The mucous layer (m) expands 

 over nearly half the yolk, and 



daw's egg 



Ibid. 



337 Anterior extremity of an em- 



bryo 



Ibid. 



becomes covered 

 little fringes. 



with many 



338 Ideal section of an embryo. 



[Ibid. 



339 342 Views of embryos mag- 

 nified . . . [Ibid. 

 343 Ideal section of ditto . Ibid. 

 344, 345 Outlines of embryos of the 



fowl . 



Ibid. 



346 View of the vitellus magnified. 



[Ibid, 

 of the 

 Ibid. 



347 View of the embryo 



yolk . 



348 Yolk of the hen's egg . Ibid. 

 349 354 Views of embryos in dif- 

 ferent stages of development. 



[Ibid. 

 355 Embryo of a lizard (Lacerto 



agilis) 



Ibid. 



317 The embryo (c) is seen sur- 



rounded by the amntos (6), and 

 covered by the large allantois 

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

 rion ; p, m, fringes of the ma- 

 trix ... 



318 One of the chalazae of a jack- 



daw's egg pulled straight. 



[Wagner 



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. nomenon . . . Ibid. 

 323, 324 The vitellus twelve hours j 359 A chain of Salpa . Ibid. 



after incubation . Ibid, j 360 An individual Salpa . Ibid. 

 325 Magnified view of the blasto- ' 361 Cercaria, or early form of the 

 Ibid. 

 Biier 



35 6 Vorticella, showing its reproduc- 



tion by buds 



Agassiz 



357 Vorticella, showing its repro- 



duction by division . Ibid. 



358 Polyps, showing the same phe- 



derma 



326 Ideal sections 



327 Yolk after eighteen hours' in- 



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. 



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 (Medusa} : a, the 

 embryo in its first stage, much 

 magnified ; b, summit, show- 

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

 tacules shooting forth ; e, 

 embryo adhering, and forming 

 6 



