HARDWICKE'S SCIENCE-GOSSIP. 



[Jan. 1, 1S69. 



FRESH-WATER PLANARLE. 



rpHESE little Hat-worms, common as they are, 

 -*- have been little noticed among the numerous 

 objects which come under the aquarium-keeper's eye ; 

 and, with the exception of Mr. Kay Lankester's 

 paper in the Popular Science Review, I can find no 

 systematic account of their habits. I have there- 

 fore set down the following disjointed notes of my 

 own, in the hope of suggesting a more extensive 

 history to others who have greater facilities for ob- 

 servation than I possess. 



The Planaria?, which are included in the class of 

 Plat-worms (Platyelminthes), and are members of 

 the order Tushellasia, may be found abundantly in 

 our streams and ponds, either gliding about or 

 clinging in a quiescent state to the inferior surfaces 

 of stones, water-lily leaves, &c. In size they vary 

 from nearly an inch in length to a mere speck, and 

 their colouring presents different tints, — rufous, 

 orange, white, black, and olive green. Locomotion 

 is effected by a continuous over gliding, similar to 

 that of the Bubble- shell (Pkysa fontinalis), but 

 swifter. The white varieties, which are far more 

 sensitive to touch than their coloured congeners, 

 will, when alarmed, contract and relax their bodies 

 violently in the attempt to progress like a leech, 

 but, though they can proceed in this way, no true 

 sucking-disc is present. Apropos of the sensitive- 

 ness of the Planarise, they often fall foul of the 

 Hydra?, but seem nowise incommoded by the contact, 

 though sometimes escaping with difficulty from the 

 grasp of the tentacles. Like many molluscs, these 

 creatures will frequently launch themselves on the 

 surface of the water with the ventral aspect upper- 

 most. When thus travelling, any disturbance of the 

 water will send them tumbling down; and I have 

 often seen them break their fall, or even remain 

 suspended by means of a delicate thread. This 

 cord is probably spun, as Dalyell and others mention 

 spinnarets as present in some species ; but it may 

 be due merely to the mucous secretion which covers 

 the body and causes the fingers to adhere slightly 

 after handling a Planaria. They are active night 

 and day ; but if the weather be cold they contract 

 themselves and cling to sheltered stones or bury 

 themselves in the ooze. In the absence of such 

 shelter they suspend themselves from the surface of 

 the water, much as the hydra is wont to do, by 

 hollowing the ventral aspect into a kind of boat. 

 The Black Planarians may be found in cold weather 

 huddled together in great numbers and in almost 

 any water ; for they are by no means particular in 

 the latter respect, and will bear changing from fresh 

 to putrid water without injury. I have not ob- 

 served, however, that the fresh-water species enter 

 the brackish water at the mouth of the same river ; 

 and on transferring some individuals from fresh to 

 slightly brackish water they apparently lost all 



power of locomotion, feebly erecting themselves on 

 either extremity and writhing about. They were 

 dead on the expiration often minutes ; and, curiously, 

 they became tough and shrivelled like shreds of 

 leather, though naturally of a semi-gelatinous 

 consistency. 



In common with the hog-louse {Asellus) and the 

 fresh-water shrimp (Gammarus), the Planaria plays 

 the role of scavenger. A dead mollusc is speedily 

 black with feasters ; and on one occasion 1 found 

 them attending the funeral of a relative, when, the 

 orthodox " baked meats " not being forthcoming, 

 they devoured their deceased friend. At another 

 time a living stickleback was attacked. The fish in 

 question was affected with a disease in the form of 

 white glandular swellings. Being placed for a few 

 minutes in a jar containing Planarise, an individual 

 of the black variety (Polycelis nigra) fixed itself on 

 one of the excrescent swellings ; nor was the fish, 

 though evidently troubled by its presence, able to 

 shake it off. I presently pushed the worm off, 

 whereupon a thin stream of blood issued from a 

 wound visible as a slight puncture on the ball. 

 Having left the fish for a short time, I found it on 

 my return covered with Planarians and, if not 

 exactly sucked dry, at least minus its natural 

 fluids. 



The aliment of these creatures is received into the 

 stomach through a suctorial pharynx, which is cap- 

 able of extension, and serves also for the ejection of 

 the non-assimilated food. The latter falls as white 

 flosculent matter. In one specimen, which I cut 

 transversely, this pharynx remained hanging to one 

 of the halves of the body in an extended state, and 

 did not fall off for about ten days, when doubtless a 

 new organ had been formed. 



It is well known that the Planaria; rival the 

 Hydra; in their susceptibility of reproduction by 

 artificial division ; but the power of spontaneous 

 fission possessed by them is yet hardly proved. I 

 have cut many both longitudinally and transversely, 

 and severed them partially or wholly, and they 

 usually formed perfect animals, but I have not 

 witnessed an instance of spontaneous separation ; 

 nevertheless the white species (Planaria lactea), 

 after being partially crushed, will discard the 

 wounded portion, and supply its place by a fresh 

 growth. The same species, if the frontlet be slit so 

 as to form two heads, presents a strange sight, each 

 head striving to pursue a separate course, which 

 is mostly diametically opposed to that of the other. 



A slight sketch of the characteristics of the com- 

 moner species may be found in the " Micrographic 

 Dictionary," where, in addition to the black and 

 white varieties, a dark grey species (P. torva) and a 

 dusky-brown species (P. brunned) are mentioned. 

 These are essentially similar in habits to the Black 

 Planaria, but are more locally distributed. Besides 

 these I have found several of an olive colour, which 



