TRANSACTIONS OF SECTION D. ' 693 



Red basal spots like those of the mimicking Pierines are in some cases found 

 in the mimicked Heliconii: this is especially the case in those that form models 

 for the Pierine genera Euterpe and Fereute. These spots are too widespread in 

 the Pierine sub-family to have arisen from imitation of the Heliconii; their 

 presence in the latter is probably due to ' reciprocal mimicry ' between distasteful 

 forms, as suggested by the author in ' Trans. Ent. Soc. Lond.,' 1894, p. 298. 



A curious ease of a mimetic group is afforded by the Pierines Euteiye critias 

 and E. bellona, together with their respective models Papilio zacynthics and the 

 Heliconii of the thel.viope group. The Papilio and the Heliconii have no close 

 resemblance to each other, but appear to be held together, as it were, by the 

 intermediate Pierines. If the Heliconii are considered as the models for the whole 

 group, the question arises why E. critias should copy a mimic, and not a very good 

 one, instead of the original distasteful model. It is more probable that here also we 

 have an instance of an ' inedible association ; ' this conclusion being strengthened by 

 the fact that a certain amount of ' give and take,' or 'reciprocal mimicry,' seems to 

 tave occurred between the Pierines and the Papilio, 



The paper was illustrated by coloured drawings of the species referred to. 



6. On Certain Principles of Progressively Adaptive Variation Observed 

 in Fossil Series. By Professor H. F. Osboen. 



7. On the Wing of Archceopteryx Vietced in the Light of that of Some 

 Modern Birds. By W. P. Pycraft. 



In this paper the author contended that certain of the Galliformes, such as the 

 common fowl and turkej' for instance, are descended from an ancestral form of 

 a strictly arboreal habit, in which the pollex and index digits were armed with 

 claws to assist in climbing as well as to save itself from falling. These claws 

 remained functional until a sufficient number of the primary (and secondary) 

 i-eiuiges had developed to convert the wing into an organ of iiight. Until this was 

 eflected, the development of these remigea nearest the wing (Nos. 8, 9, 10) was 

 arrested, so that the tip of the index digit might be left free for grasping. The 

 arrested development of the remiges referred to is the only clue we have left at 

 the present day, the claw of the second digit having been lost, whilst that and the 

 pollex are very small. These deductions were drawn from a precisely similar 

 arrangement shown by the author to exist in Ojnsthocomus cristatus, a bird which 

 shows many other unmistakably primitive characters. 



It was also pointed out that there is reason for believing that the claws of 

 Archaeopteryx were of prime importance only during a similar period of life — the 

 nestling period. A restoration in the shape of a model of the wing of Archajopteryx 

 was exhibited, in which it was shown that the remiges rested upon the third digit, 

 so as to leave the tip of the second free in a manner more or less resembling the 

 nestling condition of Opistkocomus. It was, however, pointed out by the author 

 that this digit might have supported the semiplume-like feathers seen in the fossil, 

 overlying the quill feathers. These may have possibly extended to the tip of the 

 second digit, and represented what we know as 'major ' coverts. 



8. On the Nej)hridial Duct of Owenia. 

 By Professor G, Gilson, of Louvain. 



Orvenia is a tubicolous annelid discovered by Delle Chiaje in the Gulf of 

 Naples, and especially studied by Claparede. The latest writer on its anatomy, 

 Dr. von Drasche, confesses his ignorance as to the presence or absence of the 

 nephridia, as well as to the way through which the genital products are led out of 

 the ccelom. 



