or DECAPOD CRUSTACEA. 53 



Aftei- slating in a very clear nuimier the facts he Jiad established, 

 the author draws the following couclusious. The carapax of the Bra- 

 chyura includes : 



I. The first and second normal segments represented by the epistome, 



or its anterior position, and the inter-antennary septum. 



II. The third normal segment, represented by the main body of the 



carapax, and the anterior portion of the prelabial plate or pal- 

 ate. 



III. The fourth normal or mandibular segment i-epresented by the 



posterior and outer part of the prelabial plate and the ventral 

 pieces of the carapax. 



Concerninir the caiapax of the Macroiira the author again 

 differs from ]\lihie-Ed\vards in designating the lateral and 

 posterior plates of the carapax of Astacus mandibular terga 

 instead of epimcra. After a careful comparative descrip- 

 tion of numerous foi-ms both among the Macronra and the 

 lower Crustacea {loc. cit., pp. 32-37) in which he men- 

 tions several seemingly adverse cases, the author concludes 

 that the origin of the carapax and the disposition of its 

 parts are essentially the same throughout the class. 



From the foregoing extracts it will be seen that Dana's 

 views are in advance of those of the other investigators, 

 but there yet remain several points of interest on which 

 it is desirable to collect further evidence. Both Milne- 

 Edwards and Dana have established with a high degree of 

 probability the origin of the carai)ax from the terga of the 

 mandibulary and anteunary somites, but neither of them 

 succeeded in finding a conclusive demonstration of the 

 fact. In the very young Squilla the thoracic and ab- 

 dominal segments of tlie body may, by careful dissection, 

 1)0 removed from their connection with the carapax, with- 

 out disturl)ing the relation of the parts in intimate connex 

 with the latter. In such a preparation the point of attach- 

 ment will be seen t(^ lie immediately behind the mandibu- 

 lary sternum, fig. 15, z. Since both the op//t/ialmic and 

 the antennulary segments are entire and have no connection 



