50 ON THE CARAPAX AND STERNUM 



include all, without exception, from the last thoracic to 

 the ophthalmic. * * * " At the sides of the antennulary 

 and antennary somites the rostral prolongation of the car- 

 apace is the direct continuation outward of the epimeraof 

 these somites, and there is nothing to be compared to an 

 apodeme, but the sternum of the ophthalmic somite after 

 giving off the lamella which forms the inferomedian ros- 

 trum, is prolonged on each side of the middle line back- 

 wards and outwards into a free, expanded, thin, calcified 

 process which applies itself against the carapace by its 

 upper surface, and by its under surface gives attachment 

 to the anterior gastric muscles. * * * On the dorsal sur- 

 face there is no indication of any division of the carapace 

 into terga corresponding with the sterna of the somites, 

 but it is marked by a well-defined curved groove. * * * " 

 The accompanying diagram explains his views of the so- 

 mite in Astacus. 



Milne-Edwards (2) considers the carapax in the major- 

 ity of the Decapods to consist of a single piece, part of 



s 



Diagram of crustacean segment; ep, epimerum; es, episternum; , sternum; 

 t, tergum. 



which is furnished by the antennary and mandibulary som- 

 ites respectively. This author states, that while in Squilla 

 the carapax belongs almost entirely to the antennary seg- 

 ment, in Limnetis on the other hand, it pertains chiefly 

 to the mandibulary somite. Furthermore, the tergum of 

 the antennulary segment is entirely wanting in the Deca- 



