224 THE CANADIAN NATURALIST. [June 



Squilla and a species of Gecarcinus being the only exception 

 known to me to the law that the Crustacea bear their essis about 

 "with them. Besides the structureless, dense, irregularly laminated 

 chorion, there is an inner egg membrane composed of rudely 

 hexagonal cells ; this membrane increases in size with the growth 

 of the embryo, the chorion splitting and being thrown off during 

 the latter part of embryonic life. Unlike the Crustacea generally 

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

 of the yolk, as in the spiders and scorpions, and certain Crustacea, 

 i.e., Eriphia spinifrons, Astacus JliiviatiUsf Palcemon adspersus, 

 and Crangon maculosus, in which there is no metamorphosis. 



The embryo is a Nauplius; it sheds a Nauplius skin about the 

 middle of embryonic life. 



This Nauplius skin corresponds in some respects to the "■ larval 

 skin" of German embryologists. 



The recently hatched young of Limulus can scarcely be con- 

 sidered a Nauplius, like the larvse of the Phyllopoda, Apus and 

 Branchippus, but is to be compared with those of the trilobites, as 

 described and figured by Barraude which are in Trinucleiis and 

 Agnostus born with only the head and pygidium, the thoracic 

 sesrments beins; added during: after-life. The circular larva of 

 Sao hirsuta, which has no thorax, or at least a very rudimentary 

 thoracic region, and no pygidium, approaches nearer to the 

 Nauplius form of the Phyllopods, though we would contend tha* 

 it is not a Nauplius. 



The larva passes through a slightly marked metamorphosis. It 

 differs from the adult simply in possessing a less number of abdo- 

 minal feet (gills), and in having only a very rudimentary spine. 

 Previous to hatching it strikingly resembles Trinucleiis and other 

 trilobites, suggesting that the two groups should, on embryonic 

 and structural grounds, be included in the same order, especially 

 now that Mr. E. Billings^ has demonstrated that Asaphus pos- 

 sessed eight pairs of five-jointed legs of uniform size. The trilo- 

 bate character of the body, as shown in the prominent cardiac 

 and lateral regions of the body, and well marked abdominal seg- 

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



*Proceeclings of the Geological Society of London. Eeported in 

 " ISTatnre." June 2, 1870. In this communication Mr. E. Billings an- 

 nounces the important discovery of a specimen of Asaplius platycepha- 

 his, showing that the animal possessed eight pairs of five-joined feet» 

 widely separated as their insertions by a broad sternal groove. 



