1871.] WOODWAED XIPHOSTJIiA. 53 



bryo apparently to greater advantage than Dr. Dohrn, who has given 

 us two admii'able ventral views and a much more advanced dorsal 

 aspect. 



'•' This stage is signaKzed," says Dr. Packard, " by the more 

 highly developed condition of the dorsal portion of the embryo and 

 the increase in size of the abdomen*, and the appearance of nine 

 distinct segments to it. The segments of the cephalothorax are now 

 very clearly defined, as also the division between the cephalothorax 

 and the abdomen, the latter being now nearly as broad as the cephalo- 

 thorax, the sides of which are not spread out as in a later stage." 



"At this stage the egg-shell (exochorion, Dohrn) has burst, and 

 the 'amnion.' (c7iorio?i, Dohrn) increased in size several times its 

 original bulk, and has admitted a corresponding quantity of sea- 

 water, in which the embryo revolves." 



7t7i stage. — " At ahttle later period the embryo throws off an em- 

 bryonal skin, the thin peUicle floating about in the egg." (Packard.) 



8t7i stage.—" fetiU later in the life of the embryo the claws are 

 developed, an additional rudimentary giU appears, and the abdo- 

 men * grows broader and larger, with the segments more distinct." 



9th stage. — " Just before hatching, the cephalothorax spreads out, 

 the whole animal becomes broad and flat, the abdomen *, being a 

 little more than half as wide as the cephalothorax f. The two eyes 

 and the pair of ocelli on the front edge of the cephalothorax f are 

 distinct ; the appendages to the gills appear on the two anterior 

 paii-s ; the legs have increased in length, thongh only a rudimentary 

 spine has appeared on the coxal joint, corresponding to the nume- 

 rous teeth in after life. The trilobitic appearance of the embryo is 

 most remarkable. It also now closely resembles the Xiphosuran 

 genus JBelinurus. The cardiac or median region of the head-shield 

 is prominent and convex. The lateral regions are more distinctly 

 marked on the abdomen* than on the cephalothorax f. The six 

 segments of the cephalothorax f can with care be distinguished ; 

 but the nine abdominal segments * are most clearly demarked ; and 

 in fact the whole embryo bears a very near resemblance to certain 

 genera of Trilobites, as Trinudeus, Asajohus, and others." (See 

 p. 60, figs. 21 & 22.) 



10th stage. — The young Limulus, upon emerging from the egg, 

 differs chiefly from the previous stage in the abdomen* being much 

 larger, scarcely less in size than the cephalothorax f, and in the larger 

 size of the gills. The abdominal spine is stUl rudimentary, forming 

 only a small lobe varying in length, but scarcely projecting be- 

 yond the abdomen. It forms, in fact, the ninth segment J. 



" At this stage," Dr. Packard observes, " the young swim briskly 

 up and down the jar, skimming about on their backs by flapping their 

 giUs, not bending their bodies." 



11th stage. — " In a succeeding moult, between three and four 

 weeks after hatching, the abdomen * becomes smaller in proportion 



* Thoracico-abdominal segments. — H. W. 



t Cephalic plate. — H. W. 



J This is the Trilobitenstadium of Dohrn. 



