juirrim'T structure of Podura Scales. 25 
median line with a smaller similar group on a papilla (b) just below 
it. The two other groups (c, c) lie right and left of the large cavity 
that leads to the buccal funnel, and each is the extremity of a curved 
row of large ciKa lying between the inner and outer small ones, and 
ending with them at a point (d) on the ventral surface opposite to 
the buccal funnel. Leydig places the aperture of the buccal funnel 
almost in the centre of the large cavity surrounded by the inner 
row ; but, as shown in Fig. 9 (which is an imaginary section of the 
head), the whole cavity slopes down towards the ventral surface, 
and the entrance to the buccal funnel (d) is close to it. The other 
letters in the figure refer to the same parts as in Fig. 8. Fig. 10 is 
a dorsal view of the top of the trochal disc. 
In attempting to make out the structure of the teeth either by 
crushing the animal or dissolving it in caustic potash, it frequently 
happens that the parts are so thrown upon each other that a distinct 
view is impossible ; but a few days ago I obtained a specimen capi- 
tally placed, and was able to see that the edges of the incus are 
themselves armed with fine small teeth (Fig. 11, a, a), which have 
not, I beHeve, been previously noticed, and which no doubt com- 
minute the food that has been partially torn by the larger teeth. 
In Fig. 12 are shown the muscles of a specimen that has been 
killed in bichromate of potash, and compressed so as to make the 
muscles show their points of attachment. The muscles 1 and 5 
retract the head, and so do the anterior portions of 2 and 4, which 
latter, in conjunction with 3, also act to draw in the foot ; 6 is a 
small muscular thread from the spot where the dorsal setae are 
situated to the head; and 7-12 are similar small threads that 
retain in their places the gastric glands, mastax, stomach, ovary, 
and contractile vesicle. Of course the figure only represents the 
muscles on one side of the rotifer : they all occur in pairs, and 
Fig. 13 shows how curiously they terminate in the foot. 
A rocket-shaped body carrying setae (Fig. 14) exists on either 
side of Hydatina (Fig. 16, a), just as in Triarthra; but it varies a 
little in shape from similar ones (Fig. 15) that are found at the 
extremity of Synchoeta Tremula. 
VI. — Some Bemarhs on the Structure of Diatoms and Podura 
Scales. By F. H. Wenham. 
At the last meeting of the Koyal Microscopical Society (June 9) 
this much-vexed question was again reyived, in the discussion 
following the paper read by the President. 
In consequence of the higher powers and more perfect definition 
