PLATE XXXIII. 



Order — Merostomata. 

 Sub-Order — Xiphosura. 

 Larval stages of Limulus polt/phemus, Latr. 



Figs. 



1. The embryo enclosed within its two membranous egg-envelopes, the inelastic "chorion," and the 



inner elastic " protoderm " (y). The primitive disc is seen marked off from the main yolk- 

 mass (p m), and bearing the mouth (m) and the six pairs of finger-shaped, rudimentary 

 cephalic limbs (a — -f). Copied from Dr. Packard's 'Memoir,' op. cit., pi. ; , fig. 13. 

 (P. 215.) 



2. The beginning of the " sub-zoean stage," in which two pairs of thoracic appendages ((/, h) are added 



to the six pairs seen in Fig. 1, and the appearance of segmentation on the back of the embryo 

 (p m). Copied from Packard, pi. iv, fig. 16. (P. 215.) 



3. Ventral aspect, and 4.. Side-view of embryo. The thoracico-abdominal division (t, a) is now clearly 



differentiated from the head (c), with the segments well marked. The five (or six?) lobes of 

 the liver indicating five (or six ?) cephalic somites (see Fig. 4 c), A third pair of thoracic 

 appendages are added (Fig. 4 i). Copied from Packard, pi. iv, figs. 19, 19 a. (P. 216.) 



5. Posterior view of an older individual, showing the thoracico-abdominal segments, the cephalic limbs, 



and the three pairs of thoracic branchial feet and the dorsal heart. Copied from Packard, 

 pi. iv, fig. 20. (P. 217.) 



6. The dorsal aspect ; Fig. 7, the side-view or profile ; and Fig. 8, the ventral aspect of the same 



embryo just before hatching; oc, the ocelli; o, the compound eyes; ch, the " chilaria " or 

 " metastoma ;" op, the opercular plate ; br, the branchial plate. The other letters correspond 

 with the same parts in previous figures of the earlier stages of the embryo. Copied from 

 Packard, pi. v, figs. 24, 24 a, 24 b. (P. 218.) 

 9. Ventral aspect of another embryo somewhat less advanced than Fig. 8 (copied from Dr. Anton 

 Dohrn). The " chorion " is split, and the embryo is seen to revolve within the expanded 

 " protoderm." The letters correspond with those marked on the embryos in earlier stages. 

 (P. 219.) 



10. Dorsal aspect; and Fig. 11, ventral aspect of freshly hatched young of Limulus poly phemus. Copied 

 from Packard, pi. v, figs. 25 and 25 a. (P. 220.) 



12. Nearly the same stage as the foregoing (copied from Dr. Anton Dohrn). This is Dohrn's "Trilo- 

 bitenstadium." (P. 220.) 



