ON THE PLANARLE OF OUR PONDS AND STREAMS. 
By E. RAY LANKESTER. 
T HE little creatures with the structure and history of which 
I hope in the following pages to make the reader ac- 
quainted, as far as space and the great obscurity surrounding 
them will permit, belong to a group of animals which is at 
present perhaps more under discussion among zoologists than 
any other — a group which stands alone in the anomalous 
character of some of its organs and methods of reproduction 
and development, and is remarkable at the same time for the 
many points of resemblance presented by it to several other 
large zoological groups. The great sub-kingdom Vermes or 
Annuloida is now generally recognised as embracing five large 
but subordinate classes of worm-like animals, characterised by 
their general elongate and frequently jointed form ; by the 
absence of jointed locomotive organs, the place of which is 
frequently supplied by suckers, or by soft processes bearing 
movable bristles ; by the very abundant distribution of cilia 
on the surfaces of their bodies, or of their internal organs, 
at one or other period of life; by the correlated, unstriped, 
or faintly-banded character of their muscular fibre ; by the 
primarily ventral position of their mouths ; by the absence or 
terminal position of the anus ; and by the presence of a pecu- 
liar vascular system (the water-vascular system), sometimes 
closed, but frequently communicating with the exterior, the 
fluid in which performs in part the functions of the blood of 
higher animals, and in many cases contains the same colouring 
matter as the red blood-corpuscles of man. They nearly all 
exhibit remarkable metamorphoses in growth, and reproduce by 
gemmation and fission as well as sexually ; many are internally 
parasitic. 
Of these five classes, the most highly organised is the group 
of Ringed Worms or Annulata, comprising the marine, fresh- 
water, and terrestrial bristle-bearing Worms, and the Leeches. The 
class of Wheel-animalcules (Rotifera) is by some excluded from 
the Vermes, but seems to fall naturally within the limits of the 
sub-kingdom, connecting it with the Crustacea ; other zoologists 
