492 Reports and Proceedings. 



This membrane increasing in size witL. the growth of the embryo, 

 the chorion splitting and being thrown off during the latter part 

 of the embryonic life. Unlike the Crustacea generally, the primitive 

 band is confined to a minute area, and rests on the top of the yolk 

 as in the Arachnida. The embryo is hatched as a Nauplius ; it sheds 

 its Nauplius skin about the middle of the period of its embryonic 

 life. This Nauplius skin corresponds to the " larval skin" of the 

 the German Embryologists. 



Neither does the embryo nor the larva pass through any metamor- 

 phosis.^ The larva differs from the adult in possessing a less num- 

 ber of abdominal feet (gill-feet), and in having only a very rudi- 

 mentary spine. 



Previous to hatching it strikingly resembles Trinucleus and other 

 Trilobites, suggesting that the Trilobites are lower than the XipJios- 

 ura, and that the two groups should, on embryonic and structural 

 grounds, be included perhaps in one order. 



The inferior position of the Trilobite is also seen in the ovate 

 body, like the early embryo of Limulus, the uniformity of the limbs 

 and the broad sternal groove (described by Mr. E. Billings) and the 

 embryonic abdomen. 



The trilobate character of the body, as shown in the prominent 

 cardiac region, and the well- worked (movable?) abdominal seg- 

 ments of the embryo, the broad sternal groove, the position and 

 character of the eyes and ocelli, confirm this view. 



Now that Mr. E. Billings has demonstrated that Asaplius platy- 

 cephalus possessed eight pairs of legs ^ of uniform size, the Trilobites 

 should be taken out of the neighbourhood of the Phyllopods and 

 placed at least next to Xiphosura. 



The organization and habits of Limulus throw much light on the 

 probable anatomy and habits of Trilobites. The correspondence of 

 the cardiac region in the two groups shows that their heart and cir- 

 culation were very similar. The position of the eyes shows that the 

 Trilobites had extraordinary long and slender optic nerves, and a 

 general similarity in the nervous system. The reproductive organs 

 of the Trilobites were probably very similar to those of Limulus, and 

 the eggs were doubtless laid in the sand or mud and fertilized by 

 the male after their deposition by the female. The ova probably 

 filled the large cephalophorax, as in Limulus. No doubt the Tri- 

 lobites possessed powerful muscles (as in Limulus), to enable them to 

 burrow in search of marine worms, etc., and probably the alimentary 

 canal gizzard and immense liver were likewise foreshadowed in this 

 early prototype of Limulus.^ 



^ This seems to be slightly misleading, since Dr. Packard's own statement speaks 

 of important changes taking place in the larval king-crab before it arrives at the 

 adult condition. — Edit. Geol. Mag. 



- See Report of Mr. E. Billings's paper, "Notes on some Specimens of Lower 

 Silurian Trilobites " (read before the Geological Society of London May 11th, 1870) 

 Geol. Mag., 1870, Vol., VII., June, p. 291. 



3 See also an excellent article on " The Horse-foot Crab," by the Eev. S. Lock- 

 wood, Ph. D. in the American Naturalist, vol. iv.. No. 5, for July, 1870, p. 257. 



