620 F. H. GRAVELY. 
Korschelt, 1893, pp. 237-242, Pl. XIII, figs. 12-15) ; in this form 
the appendages project and bear permanent sete at quite an 
early stage (Korschelt, loc. cit., fig. 5), as in other larvee of 
the Nereidiformia, however. When the cirri develop is not 
definitely stated, but it would appear to be very soon after 
the stage shown in Korschelt’s fig. 15, when the first pair of 
appendages only is present, for he says (p. 240) of this stage, 
“von den Cirren ist an den Parapodien noch nichts zu 
bemerken; sie erscheinen am freien Knde abgestumpft ;” 
and states on p. 242, “ Das Stadium der fig. 15 kann man als 
das Uebergangstadium der Larve in den Wurm bezeichnen.” 
The simultaneous appearance of a small number of “ pri- 
mary” segments is almost certainly a secondary type of 
development derived from a condition such as that found in 
Ophryotrocha, and it is noteworthy that this sporadic 
appearance in the Nereidiformia of the primitive method of 
segmentation of the body occurs in a species whose adult 
retains the segmental ciliated bands of the larva. 
The above characteristics of larvee of the Nereidiformia may 
perhaps be due to the strong tendency shown by worms of this 
order for a few anterior segments to bear special tentacular 
cirri—often with the suppression of the cheetigerous rami of 
their parapodia. ‘This tendency for several segments to take 
part in the process of cephalisation may very easily be con- 
nected with the way in which in Nereidiform larve the 
developmental activities are at first entirely concentrated in 
quite a small number of “primary”? segments, the develop- 
ment of succeeding ones being delayed until the appendages 
of the primary segments have acquired their full complement 
of parts. ‘The same sort of thing occurs in the larve of the 
decapod Crustacea, in which during the Zoea stage there is a 
sharp distinction between the functional appendages anterior 
to (and sometimes including) the third maxillipede, and the 
appendages posterior to this, which are all rudimentary or 
absent (see Korschelt and Heider, ‘Text-book of Embryology: 
Invertebrates, Part II, pp. 249, 250). As these larval 
characteristics of the Nereidiformia are, therefore, probably 
