212 
VII. Gills—Examine one of the gills about the 
middle of the series. Note its attachment to the body 
wall, its basal webbing, the main trunks and_ their 
branches. Remove the gill to a slide and examine it 
under a low power to see the mode of branching and the 
blood-vessels. | Note the small size and simple character 
of the first gill. 
VIII. Setz.—Notopodial sete may be easily obtained 
from a dissected specimen by taking hold with the forceps 
of the inner end of the setal sac and drawing it inwards. 
In this way the whole bundle of notopodial sete will be 
removed. ‘To clean off the tissues of the setal sac and any | 
adhering strands of muscle the preparation may be 
warmed in 5 per cent. caustic soda. After washing in 
water the setee may be placed in glycerine for a time and 
then permanently mounted in glycerine jelly. Only 
unworn sete should be selected for examination. 
By treatment of an excised neuropodium with warm 
caustic soda the muscles become gradually softened, and 
by the aid of a pair of needles may eventually be separated 
into an anterior and a posterior mass, between which the 
cheetee lie. With care the entire band of neuropodial 
cheete may be obtained. It should then be washed in 
water, placed for a time in glycerine and mounted in 
glycerine jelly. The various stages of formation of the 
new cheetwe at the ventral end of the series may be seen. 
There are usually two or three fully developed crotchets 
which have not yet come into use. These should be 
selected for observation of their characters as they are 
uninjured by wear. 
I have found it very useful to have dissections 
of small specimens, 17 to 50mm. long, for the study 
of young nephridia, which are too small to be easily 
removed from the body wall, gonads, blood-vessels, &e. 
