28 On Pterodina valvcda. 



I could not help remarking that for rotifers possessing two more 

 than usually eye-looking red spots, they steered very hadly, and 

 came very frequently into collision with each other. When too they 

 were holding on to the stems with their sucking disks, if one was 

 alarmed it instantly contracted its retractile foot, and flattened itself 

 close to the stem, at the same time withdrawing its ciliated head. 



But my attention was now arrested by the fact, obvious enough 

 even under this low power, that I had two distinct species before 

 me. One was my old friend Pterodina patina, but the other was 

 a much more beautiful creature : it had a remarkably transparent 

 lorica ornamented round the edge with bosses placed at regular inter- 

 vals like those on an ancient shield, and there were two powerful 

 transverse muscles which I had never seen in P. patina. A mo- 

 ment or two afterwards I saw, to my astonishment, one of the new 

 species sailing by, with its lorica folded down just like the flaps of 

 a Pembroke table, so altering its outline that it scarcely seemed 

 to be the same animal. A friend who was sharing my delight in 

 this novel exhibition, saw the rotifer sailing first with one flap (if 

 I may call it so) folded down and then the other ; but this I was 

 not fortunate enough to see, though I have seen P. valvata (as I 

 propose to term itj frequently with both folded at once. 



Both species lived in my miniature tank for nearly a fortnight, 

 and swarmed so that parts of its sides looked hke frosted glass : but 

 I noticed that they always avoided the hght, and that when I pur- 

 posely placed the tank with one end in a dark corner, that corner 

 soon contained nearly the whole of them. 



As I had hoped, there always were some among the number 

 placed simultaneously on the compressorium, that soon adhered to the 

 upper glass ; and upon these I could bring down the higher powers. 



The most striking peculiarity of the new species is the presence 

 of the large transverse muscles for folding the lorica. The lorica is 

 oval and nearly plane, except on its under-surface, along its major 

 axis ; where it carries a sub-conical case, in which lie the greater 

 part of the softer portions of the rotifer. 



The base of the cone is the opening from which the rotatory 

 head is protruded, and the lorica is here sht as shown in Fig. 5, to 

 give free play to the head, while the muscles (Fig. 1, n, n) close 

 the flaps of the slit when the head is drawn within the lorica. At 

 a distance from the head of about two-thirds of the length of the 

 lorica, there is a circular opening through which the false foot is 

 protruded and withdrawn. 



The water vascular system with three tags on each side can be 

 plainly seen ; but there is no contractile vesicle. There are, how- 

 ever, two objects (Fig. 1, c, c) which appear to be expansions of the 

 canals, and possibly answer the purpose of the contractile vesicle : I 

 cannot say, however, that I ever saw them contract. 



