TITANOSOMA AND POLYMICRODON IN ENGLAND 157 



studying the growth of these organs. In the last few years 

 I have repeatedly dealt with this increase of the antennal 

 joints in the larvae, and in connexion with the larvae of 

 Thaumaporatia 1 I came to the following conclusion: "a 

 comparison of the first larva with the adults and with the later 

 stages of development shows that the later seven-jointed 

 larval antennae arise from the five-jointed through the division 

 of the second and third joints." It may be pointed out as 

 particularly interesting that the process of growth in the 

 antennae of Titanosoma is somewhat different : in this genus 

 it is not the second and third joints, but the first and 

 second which undergo division. For whilst in the first larva 

 .of Thaumaporatia the first joint of the antenna is extremely 

 short and disc-shaped, and therefore very unsuited for a later 

 division, the second joint is not only very slender, but shows 

 already a clear indication of a later constriction, and in the 

 third joint the slender basal third also points to a subsequent 

 segmentation. 



In Titanosoma on the contrary the first antennal joint of the 

 first larva is not only decidedly larger, but it indicates clearly 

 that a division is to follow, in that it shows externally an 

 obtuse-angled nick. Behind this nick it bears bristles, in 

 front of it it is naked. The somewhat club-shaped second 

 joint is scarcely longer than the first, and already bears above 

 the end a sense organ. The third joint is obviously identical 

 with the sixth joint of the adult antenna — not only in its 

 spherical shape, but also in its great width and in the 

 possession of a group of sense organs. Now since in the 

 adult antenna the sense organs appear on the fifth and sixth 

 joints, it appears perfectly plain that in Titanosoma the whole 

 increase in the number of antennal joints takes place in the 

 basal half. And since the first larva with five-jointed antennae 

 is followed by a second larva with seven-jointed antennae, it 

 appears that the latter arise from the former through the first 

 and second joints being each divided into two by a transverse 



1 See Nova Acta der deutschen Academie der Naturforscher, Halle, 

 1910, pp. 116- 117. 



