370 Prof. E. Eay Lankester on the 



and of the migrated svibstitutional antennaj (postoral appen- 

 dages whicli have become prteoral) of the Crustacean series. 



V. With regard to the fundamental theory on which 

 these views as to the difference of the nature of the antennae 

 in Crustacea on the one hand and in Peripatus, Hexapods, 

 and Myriapods on the other hand depend, namely the theory 

 that a forward movement of limbs or appendages belonging 

 to body-segments has taken place in the Crustacea, so as to 

 make appendages which were originally postoral actually 

 prffioral, it appears that my publication in 1873 in the Ann. 

 & Mag. Nat. Hist., entitled " The Primitive Cell-layers of 

 the Embryo as the Basis of Genealogical Classification of 

 Animals," contains its first expression, and is anterior to 

 the adoption of any such view by Prof. Claus even in regard 

 to the limited sphere of application offered by the second pair 

 of Crustacean antennae. I do not find this theory of the move- 

 ment forwardsof a pair of postoral limbs so as to become prasoral 

 antennai expressed in the editions of Prof. Claus's '■ Grundziige 

 der Zoologie ' which preceded the publication of my sugges- 

 tion on this subject, nor has he clearly formulated it until the 

 present occasion. In the Ann. & Mag. Nat. Hist for May 

 1873, p. 336^ I wrote : — " Much more likely, it seems, is the 

 explanation that the oral aperture shifts position, and that the 

 ophthalmic segment alone in Arthropoda represents the pro- 

 stomium, the antennary and antennular segments being 

 aboriginally metastomial and only prostomial by later adapta- 

 tional shifting of the oral aperture." 



VI. With regard to the one point in the morphology of 

 the Arthropoda in regard to which Professor Claus has 

 refrained from adopting my views I may say a few words. 

 The difference between us is this : I have suggested that both 

 the first and second pairs of Crustacean antennas were originally 

 postoral appendages (limbs of tlie body-segments), and have 

 nothing to do with the prostomium. Professor Claus holds 

 that the first pair of Crustacean antennfe are truly prostomial 

 and comparable to the Annelids^ prostomial tentacles, whilst 

 he has adopted my theory of 1873 in so far only as the second 

 pair of antennae are concerned. 



There are reasons for and against each of these views as to 

 the nature of the first pair of Crustacean antennae. But I 

 will here only observe that, in accordance with my view of 

 their nature, the fact that the first pair of appendages must 

 have shifted forward at an earlier period in ancestral history 

 than the second explains in a large measure the closer and 

 more constant association of their nerve-supply with the 

 cerebral ganglion and their somewhat greater departure from 



