58 



ON THE CAKAPAX AND STERNUM 



somite. From embryological evidence it appears very 

 probable that these pieces originate as simple projections 

 of the outer posterior angle of each sternal plate and that 

 they are apparently cut off by the appearance of false su- 

 tures at a later period of development. The figures illus- 

 trating this point (figs. 18, 19, 22) hardly need any 

 explanation beyond that given in the description of the 

 plates. A comparison of figs. 18 and 22 is conclusive. 



BIBLIOGRAPHY. 



1. Huxley, T. H. Anatomy of Invertebrated Animals (chapter on Crustacea). 



London, 1878. 



2. Milne-Edwards. Observations sur le Squelette T6gumentaire des Crustacea 



D^capodes et sur la Morphologic de ces Animaux. Ann. Sci. Naturelles 

 Ser. 3e, T. XVI, pp. 221-291. Pis. 8-11. Paris, 1851. Consult also Legons 

 sur 1'Anat. et la Phys., etc., T. 10, p. 212. Paris, 1872. 



3. Owen, K. Lectures on the Comparative Anatomy and Physiology of Inverte- 



brate Animals, p. 301. London, 1855. 



4. Dana, James D. Homologies of the Carapax among Crustacea. U. S. exploring 



expedition, 1838-'42, Vol. XIII, pp. 23-28, 32-35. Atlas, pi. 11, fig. 9d and 16, fig. 

 9c. Philadelphia, 1852. Also On the markings of the carapax of Crabs. 

 Amer. Journal of Science and Arts, 2d Ser., Vol. XI, p. 95. (Jan., '51.) 



EXPLANATION OF PLATES II AND III. 



REFERENCE LETTERS. 



a antennule n 



a' antenna o 



as antennular sternum os 



it's antennal sternum pg 



a't antennal tergum 



a'tp plates of antennal tergum r 



ap appendage s 



e epimeral plate sp 



e' epimeral groove t 



f labrum tht 



g plate covering green gland y 



g' plate between antennule and car- 

 apax x 



m maudibular skeleton 



mem membrane z 



ms mandibular sternum 



mi mandibular tergum 



mp anterior mandibular epimeral 

 plate. 



Fig. 1. Ventral view of carapax of an immature Platyonichus ocellatus, caustic 

 soda, acetic acid preparation; natural size. 

 Fig. 2. Ventral view of the earapax of Etisus dentatus; natural size. 



membranous space 



eye or orbit 



ophthalmic sternum 



processes for attachment of gastric 



muscles 

 rostrum 

 sternum 

 sternal piece 

 tergum 



thoracic tergum 

 suture between mandibular and 



antennal sternum 

 suture between epimeral and tergal 



plates of mandibular segment 

 point of attachment of carapax to 



body 



