348 



segment. The similarity is so striking that on a cursory examina- 

 tion of the young Hesperoctenes I did not at once notice that 

 the two halves of the comb were placed on the two antennae 

 instead of on the underside of the head. This comb disappears 

 in the next moult, or rather, is replaced by small spines directed 

 distad. One of the individuals with such an antennal comb 

 shows already under its skin the true guiar comb of the next 

 stage in the metamorphosis of this specimen. These observa- 

 tions are of some weight, inasmuch as they prove that an organ 

 so persistent as the guiar comb — which is present in all the 



Fig. io. — Head of larva of Hes- Fig. ii. — Head of male of Hes- 



peroctenes impressus Horv., underside. peroctenes impresses Horv., underside. 



known Polydenidœ, adult and immature, with the exception of 

 that one early larval stage of Hesperoctenes, even being present 

 if the dorsal and antennal combs are all absent, and therefore 

 might be regarded as a more ancient acquirement than the 

 other combs — is not necessarily everywhere the first to appear 

 in the ontogeny of the species of the family, and, inversely, 

 that the organ appearing first in the ontogeny of some of the 

 species is not necessarily to be considered as phylogenetically 

 older for the family than homologous organs which appear at 

 a later ontogenetic stage. However, we may nevertheless 

 assume that in the ancestral Hesperoctenes the antennal comb 

 was the first to appear, and in the ancestral Polyctenes and 



