ZOOLOGY. 



581. Finally, tin 1 division of Crustacea called xipho- 

 sura is composed only of a single genus, that of the limulus, 

 whose structure is most anomalous. These are large crus- 

 tacea, whose bodies are divided into two parts ; the first, 

 covered by a semicircular buckler, 

 has eyes, antennae, and six pairs of 

 feet surrounding the mouth, which 

 serve at the same time for walking 

 and for mastication (Fig. 121) ; the 

 second portion of the body, covered 

 by another buckler, almost tri- 

 angular, carries beneath, five pairs 

 of swimming limbs, whose posterior 

 aspect is covered with branchiae ; 

 and it terminates "with a long 

 styliform tail. These singular ani- 

 mals inhabit the Indian Ocean and 

 the coasts of America; they are 

 known by the common name of 

 Molucca crabs. 



[" As there is scarcely a subject 

 more interesting in natural history 

 than that part of it which treats 

 of the various metamorphoses which 

 all animals undergo in their pro- 

 gressive growth from the em- 

 bryonic to the adult condition, 

 I have ventured to subjoin the 

 observations made on this subject by a former most esteemed 

 student of mine, and a careful observer.* They refer, no 

 doubt, especially to the class cirrhipeds, but mutatis mutandis 

 apply to all. In my late inquiries into the dentition of 

 the salmon, other singular facts have come out, plainly dis- 

 proving the opinion of M. Valenciennes, that ' Naturalists 

 have only to do with the adult forms.' For all these adult 

 forms or species are included in the history of the young, 

 as I have proved with regard to the salmonidae ; whilst ail 

 transcendentalists since the time of Goethe and Oken have 

 known that the larva conditions of many living species 

 tvpify, or are types of, adult forms or species now extim-t ; 

 that is, of the adult forms of the fossil world. Thus it 

 is that the history of the organo-genesis, of the metamor- 



Mr. Henry Goodair, in the Edinburgh Philotophical Journal. 



Fig. 437. Limulus. 



