Endopodal portion of limb, with — < 



414 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



The nomenclature and synonymy of the parts of the Crustacean limb 

 in general may, then, be tabulated as follows : 



( Epipodite, flabellura, scapliognatliite, gill-scraper, giU-fan. (In Limnadia 

 Epipodal portion of limb .. < upper or dorsal (br) part (oviger) ana lower (&/•'). 

 (Branchia, gill. 



' 6 endites in Phyllopod thoracic legs. 

 5 endites in 2d maxilla of Astacns and Sergestes. 

 4 endites in 1st masillipede of Astacns and Sergestes. 

 2 endites (5th and Gth endopodite and exopodite) in 3d maxilli- 



pede of Aetacus and Homarus. 

 1 endite ? (=5thPhjlIopod endite?) in thoracic leg of Homams and 

 Astacus arising from a 2-iointed axis or protopodite (consisting 

 of coxopodite and babipodite), to which are appended 

 (a) epipodite and brauchia. 



f 5 dactylopodite. 



(&) (endopodite) the leg in Decapoda with 5 ] \ ^^^^^^^hVa 

 joints. 1 o ♦'"rpoponite. 



■' 2 meropodifce. 



(, 1 ischiopodite. 



The carapace. — This is seen, when we study the development of the 

 Phyllopods, to originate in the Nauplius as the undifferentiated covering 

 or tergal portions of the first and second and mandibular segments of 

 the Nauplius, which become enlarged during the successive moults 

 of the animal until, as in JEstheria or Limnadia^, it may cover the 

 entire body. In adult life it becomes bivalvular and is attached to 

 the body by the adductor muscle, which is situated in the mandibular 

 segment, the prae-oral part of the head in the Limnadiad^B and Apodidw 

 being more or less diflerentiated from the carapace proper. 



As long ago pointed out by Professor Dana, the carapace of the De- 

 capoda (the lobster for example) is a development of the tergal portion 

 of the second antennal and mandibular segments. The development 

 of Penwus and Eupliausia from the naujjlius to the adult confirms the 

 view that the caraj^ace is originally the antennal and mandibular tergites 

 which form a single carapace and finally covers the cephalothorax of 

 Decapoda. That no part of the carapace represents the thorax is 

 seen in the zoeal carapace which covers the front part of the body before 

 the thoracic segments are developed. 



HOMOLOGY OF THE EYES. 



When we consider the nature of the compound eye of the Cladocera 

 and Phyllopoda and study the mode of development of the cornea from 

 epidermal cells, we see that the eye-stalk of the Brauchipod eye is 

 sirai^ly an unjointed iDrotuberance of the first antennal segment, and 

 can in no way be regarded as the homologue of a jointed appendage. 

 Moreover, the embryology of these Crustacea shows that the compound 

 eyes are developed upon the tergal part of the first segment of the head, 

 and that there are no traces of a pree-antennal segment. 



In the Decapoda our unpublished observations on various zoese {Lupa^ 

 Palccmon and Tozeuma caroUnensis), as well as the data given by those 

 who have written on the embryology and metamorphosis of Decapods, 

 all show that the faceted stalked eyes of Decapods should not be re- 

 garded as homologues of the legs, although eminent authorities, such 

 as Huxley, Claus and others, regard them as being the morx^hological 

 equivalent of the succeeding jointed members. In Tetradecapods the 

 comiwund eyes are invariably sessile. In the Merostomata, Limulus, as 



1 In Limnadia, as shown by Lereboullet (see Fig. 43), and in Estheria, as stated by 

 Claus, the carapace valves apparently arise from a j^ost-mandibular segment, but this 

 is exceptional amoug the Phyllopods. 



