516 HENRY M. BERNARD, 



that the. trachea' are also homologous with setiparous glands; and these, 

 owing to their nietameric arrangement and position on the body we 

 specify as the acicula r glands of the dorsal parapodia of the original 

 Tracheatan-Annelid. 



The row of homologous structures is, however, by no means ex- 

 hausted. Assuming the antenna) to have originally belonged to the 

 1st segment, three pairs of parapodia, viz. those of the 2nd, 3rd and 

 4th segments moved forward in the original Tracheatan-Annelid to 

 form the Hexapodan jaws and maxilla; round the anteriorly placed 

 mouth. The twist round of each parapodium first of all from the 

 vertical into the horizontal plane, and secondly in the horizontal plane 

 towards the anterior end of the body, would allow of both branches of 

 the parapodium being used, the ventral as the jaw, the dorsal as palp. 

 And so, as a matter of fact, we find that the head limbs of the Tra- 

 cheata are almost invariably biramose. In the course of their deve- 

 lopment (cf. Fig. 2) they show from the first a much greater similarity 

 to broad leaf-like parapodia than do the rudiments of the specialised 

 ambulatory legs which, we believe, represent only one, viz. the ventral 

 branches of the original parapodia. 



Thus the whole parapodium being turned round, the acicular glands 

 (either dorsal or ventral, probably the latter) would naturally also come 

 to point forward, a position from which but a very slight displacement 

 would cause them to open in the mouth. 



In the Antennata we find, as we should expect from this derivation 

 that the salivary glands often occur in as many as three pairs. 



This homology of the salivary glands of the Hexapoda with the 

 trachea; is not new. CAitRiiniE ^), from his study of the embryology of 

 Chdlicodoma muraria, goes even further, and claims not only the sali- 

 vary glands but also the tentorium as homologous with trachea;. It 

 is obvious that a deduction of them all from acicular or setiparous 

 glands explains these homologies. I have also endeavoured elsewhere 2) 

 to show that the salivary glands of J^pws are acicular glands; spinning 

 glands arc well known developments of setiparous glands, and it is 

 difficult to see why the trachea; should not also he deduced from si- 

 milar structures. 



If this view of the origin of the salivary glands from acicular glands 

 be correct, it shows that the Protracheata form an isolated group, be- 



1) Carrièrk, Arch. f. micr. Anatomie, vol. 35, p. 1890. 



2) cf. reference at the foot of page 533. 



