Plate III. 



AU the figures (Figs. 34-53), with the exception of Fig. 61, 

 were drawn front life as if they were opaque bodies, (though 

 in reality they loere much more transparent), in order to show 

 the external changes during these stages. 



Fig. 34. — Embryo a little advanced from the gastrula, and with the 

 mesentohlastic cell mass, (side view), from life, x 310. 



Fig. 35. — Embryo with the arm-ridge and the mantle-fold (seen from the 

 anterior face), x x Depressions on the mantle fold which are to 

 double it into the two mantle lobes, x 370. 



Fig. 36. — Same embryo, seen from the future dorsal or ventral side, x 370. 



Fig. 37. — Embryo a little more advanced than that of Fig. 35. x x De- 

 pressions have become deeper. The stomodteum has appeared (an- 

 terior view), x 370. 



Fig. 38. — Embryo at the same stage as Fig. 37 (seen from the anterior 

 and ventral sides) slightly compressed, x 310. 



Fig. 39. — Embryo a little older than Fig. 38, in which the mantle lobes 

 have formed (dorsal view), x 370. 



Fig. 40. — Embryo at nearly the same stage as Fig. 39 (side view). x 370. 



Fig. 41. — Embryo at nearly the same stage as Fig. 39, compressed a little 

 (ventral view). In this we see the arm-apparatus ciliated, x 310. 



Fig. 42. — Embryo of the next stage with semicircular mantle-lobes (ventral 

 view), x 370. 



Fig. 43. — Embryo of a stage similar to that of Fig. 42, (side view). The 

 mantle lobes have greatly increased anteriorly, x 370. 



Fig. 44. — Embryo of the next stage with the Anlagen of the tentacle and 

 the first pair of cirri. The mesoblast cell masses are clearly seen 

 (ventral view). x 370. 



Fig. 45. — Embryo of the same stage as the last figure. The rupture of 

 the vitelline membrane is seen (dorsal view), x 370. 



Fig. 46. — Embryo a little more advanced with the Anlagen of the second 

 pair of cirri (seen from the anterior and ventral sides), x 370. 



Fig. 47. — Same embryo (seen from the left side and ventral face), x 370. 



Fig. 48. — Embryo of nearly the same stage as Fig. 46, showing that the arm- 

 apparatus is attached to the dorsal mantle (seen from the anterior 

 face). The ventral side is placed downward in the figure, x 370. 



Fig. 49. —Embryo a little older than Fig. 46, with well developed tentacle 

 and two pairs of cirri (dorsal view), x 370. 



Fig. 50. — Embryo of a stage similar to that of the preceding figure. A 

 pair of coelomO sacs can be seen (ventral view), x 370. 



Fig. 51. — Embryo of about the same stage, from a preserved specimen, x 3S0. 



Fig. 52. — Embryo with three pairs of cirri, — the oldest of all the embryos 

 I was able to rear from the egg (ventral view), x 370. 



Fig. 53. — Embryo of the same stage as the last figure, whose arm-apparatus 

 is stretched out and is about to swim, (in natural colors) x 370. 



