145 
a large number in the neuropodia of the branchial region. 
One of the neuropodia of a specimen only about six inches 
long contained 110 fully formed cheetee and eight or nine 
others in course of formation at the ventral end of the series. 
The crotchets show considerable differences according 
to the age of the specimen from which they have been 
taken. Those of post-larval specimens (5'1 mm. long) are 
‘03 to ‘04 mm. long, and bear two, or occasionally three, 
sharply marked teeth behind the rostrum and also a well- 
marked process, ending in a fine point, under the rostrum 
(fig. 15). In older specimens 17 mm. long, which have 
assumed the adult characters and mode of life the 
crotchets are ‘1 to ‘12 mm. long, and bear two well-marked 
teeth. Specimens about 100 mm. long have cheete which 
are ‘4 to ‘5 mm. long, each of which bears two or three 
very small teeth and also a very small subrostral process. 
The crotchets of large specimens, especially those of the 
Laminarian variety, may attain a length of ‘85 mm. 
From the time of their formation they are devoid of teeth, 
but bear a rather blunt subrostral process. It is inter- 
esting to note that as the animal grows in size the rostrum 
of the crotchet, which in the post-larval stages is at right- 
angles to the shaft, in later formed chietze makes a con- 
siderably greater angle with the shaft, the angle 
increasing with the age of the worm from which the 
cheete are obtained, so that in a cheta from a large worm, 
e.g., a Laminarian specimen about 250 mm. long, the angle 
between the rostrum and shaft is almost 130°. Concur- 
rently there is a reduction in the size of the teeth of suc- 
cessive generations of chet, so that although in post- 
larval stages the teeth are large and comparable to the 
rostrum in size, they are entirely absent from the chete 
of very old specimens. (For method of isolation and 
preparation of sete, see under practical work). 
L 
