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POPULAR SCIENCE REVIEW. 
Fig. 15. Tenth stage, in which eight free segments succeed the head, and 
three soldered segments form the pygidium. [In the twentieth 
stage figured by Barrande the adult has seventeen free 
thoracico-abdominal segments and two soldered ones (the 
pygidium).] 
„ 16. Egg of Limulus polyphemus : a, the chorion ; b, the exochorian 
(after Dohrn *). 
„ 17. Third stage in the embryo of Limulus : a, chorion ; b, exochorion 
(after Packard t). 
„ 18. Fourth stage (?) in the embryo of Limulus (after Dr Packard’s t 
figure). 
„ 19. Fourth stage (?) in the embryo of Limulus : 1, antennules ; 2, 
antenna ; 8-6, maxillipeds ; 7 and 8, thoracic plates afterwards 
bearing the branchiae j m, the mouth ; x, the ovarian apertures 
(?) ; a , the abdomen (after Dohrn *). 
„ 20. Fifth stage (?) of embryo of Limulus (after Dohrn *). At this 
stage the exochorion is split, and the chorion is expanded by 
the admission of water by endosmose, in which the embryo is 
seen to revolve. 
„ 21. Ninth stage (?) of embryo, ‘just before hatching’ (after Pack- 
ard f) : dorsal aspect. 
„ 22. The same : side view of embryo. 
„ 23. Larva of Limulus recently hatched (after Packard f). 
,, 24. Larva of Limulus on hatching (the u Trilobitenstadium *’ of 
Dohrn *). 
* “ Zur Embryologie und Morphologie des Limulus polyphemus'' Von 
Dr. Anton Dohrn. (Jenaische Zeitschrift, Band vi. Heft 4, p. 580, Tafeln 
xiv. xv.) Received September 30, 1871. 
f “ On the Embryology of Limulus polyphemus By A. S. Packard, 
jun., M.D. Read before the American Association for the Advancement of 
Science, August 1870. (“American Naturalist,” vol. iv. No. 8, 1870, 
October, p. 498.) 
