EXPLANATION OF THE FIGURES. 15 



Fio. 



veloped, and bent upwards. The upper part of the yol* (d d ) is 

 nearly separated from the yolk sphere, and is to become the in 

 testine. The heart (h) is already distinct, and connected by 

 threads with the blood-layer of the body. 



127. Section of the egg of a mammal ; v, the thick vitelline membrane, 



or chorion ; y, yolk ; s, germinative dot ; g, germinative vesicle. 



128. The same, showing the empty space (k) between the vitelline sphere 



and chorion. 



129. Shows the first indications of the germ already divided in two layers, 



the serous layer, (s,) and the mucous layer, (m.) 



130. The mucous layer (m) expands over nearly half of the yolk, and be- 



comes covered with many little fringes. 



131. The embryo (e) is seen surrounded by the amnios, (b,) and covered 



by a large allantois, (a;) p e, fringes of the chorion ; p m, fringes 

 of the matrix. 



132. Hydra, showing its reproduction by buds. 



133. Vorticella, showing its reproduction by division. 



134. Polyps, showing the same. 



135. A chain of Salpae. 



136. An individual salpa ; m, the mouth ; a, embryos 



137. Cercaria, or early form of the Distoma. 



138. Distoma, with its two suckers. 



139. Nurse of the Cercaria. 



140. The same, magnified, showing the included young. 



141. Grand nurses of the Cercaria, enclosing the young nurses. 



142. Stages of development of a jelly-fish, (Medusa ;) o, the embryo in 



its first stage, much magnified ; 6, summit, showing the mouth ; 

 C;/ ff, tentacles shooting forth ; e, embryo adhering, and form- 

 ing a pedicle ; h, i, separation into segments ; d, a segment be- 

 come free ; k t form of the adult. 



143. Portion of a plant-like polyp, (Campanularia, ) a, the cup which 



bears tentacles ; b, the female cup, containing eggs ; c t the cups 

 in which the young are nursed, and from which they issue. 



144. Young of the same, with its ciliated margin, magnified. 



145. Eye of the perch, containing parasitic worms, (Distoma.) 



146. One of the worms magnified. 



147. Transformations of the canker-worm, (Geometra vemalis ;) a, the 



canker worm ; b, its chrysalis ; c, female moth ; d, male moth. 



148. Metamorphoses of the duck-barnacle, (Anatifa;) a, eggs, magnified; 



b, the animal as it escapes from the egg ; c, the stem and eye ap- 

 pearing, and the shell enclosing them ; d, animal removed from 

 the shell, and further magnified ; e,f, the mature barnacle, affixed. 



149. Metamorphoses of a star-fish, (Echinaster sanguinolentus,} showing 



the changes of the yolk, (e ;) the formation of the pedicle, {/;) 

 and the gradual change into the pentagonal and rayed form. 



