88 THE ROTIFERA. 



water zoophytes, wisely making use of the stronger currents produced by the ciliated 

 tentacles of their hosts, in order to bring grist more easily to their own mills. I have 

 had sometimes quite " a happy family " of them in the field of view at once ; a Brachionus, 

 a Philodina or two, and a MeUcerta, all attached to the neck of a Plumatella, and all 

 eagerly whirling their wheels in order to divert to their own throats a portion of the 

 currents that swept down to them from above. Nor was this all ; for the MeUcerta in 

 its turn had the top of its tube turned to the same use, and bore, as closely under its 

 wheels as possible, the tiny case of one of its own offspring. 



Limwias ceratophylli and MeUcerta ringcns carry this semi-parasitical habit to a 

 great extent. Clusters of two or three generations all attached to one tube are not at 

 all uncommon in the former species ; and I once found in Nailsea pond a large Lim- 

 nias bearing up no fewer than fourteen of its own descendants. MeUcerta ringens, too, 

 in America, 1 is frequently met with in large adhering clusters, but in England it is 

 usually a solitary species. However, this is not invariably the case ; for not long ago I 

 had the pleasure of seeing as many as thirty-four live MeUcerta' attached to one another. 2 

 They were of all ages and sizes, and were grouped round one large tube, so as to form a 

 striking example of a natural co-operative society. Nor is this the only way in which the 

 Ilotifera show their capacity for fighting the battle of life. Every animal is limited by its 

 own powers to a certain space, beyond which its excursions cannot possibly extend. 

 Its food and its mate must be foimd within these limits ; and when these two imperious 

 wants are satisfied, there is but little time or strength left for travelling. But it would be 

 an obvious advantage to many creatures if they could be carried about from one spot to 

 another without tiring their own muscles — ready to slip off, at any favourable opportunity, 

 " to fresh woods and pastures new." Now this is precisely what some of the Brachioni 

 and Philodince contrive to do ; for they may be seen riding in clusters on the backs and 

 sides of the Entomostraca, or thickly fringing the legs and side plates of the water wood- 

 louse. 3 



Whenever I have caught a water-flea 4 so encumbered, and have placed it in a live 

 box to see the Botifera it carried, they have soon deserted their captive steed, and have 

 swum off as if to search for a more serviceable one. 



There are, too, some Eotifera whose structure has been adapted to give them a good 

 grasp of their host, or even to enable them to pierce its skin, and so suck its juices for 

 their own support. 



Balatro calvus, for example, has been found 5 in the Seine (Canton de Geneve) 

 creeping on the bodies of small water- worms which it habitually infests, and having two 

 greatly enlarged foot-processes, which probably enable it to take a firm hold. 



Another Kotiferon, C'alUdina parasitica, is always found attached to the thoracic 

 or abdominal appendages of the fresh-water shrimp 6 and water wood-louse, and limits 

 its journeyings to creeping about on the body of its host ; while the strange creature 

 Drilophaga Bucephalus holds on by its altered jaws to the hind segments of a fresh- 

 water worm, Lumbriculus variegatus, and sucks the animal it clings to. 



This parasitic Kotiferon was discovered in North Bohemia in the great pond at Hirse- 

 berg, in the banks of which the Lumln iculus is found in immense numbers. The worm 

 buries the fore part of its body in the mud, and moves its naked hinder segments like a 

 pendulum in the water. But no such gentle motion will unfasten the grip of the 

 Drilophaga, which is so firmly attached to the worm's skin that it can be dislodged only 

 by using considerable force. 



1 I am indebted to Mr. Galloway C. Morris, of Philadelphia, U.S., for this information. A cluster 

 of tubes that he sent to me contains twenty-eight specimens of various sizes adhering together. 



- It was found near Clifton by Mr. E. C. Bousfield, and is drawn in PI. V. fig. 1, e. 



" Ascllus vulgaris. ' Daphnia pulex. 



•'• By M. Ed. Claparede. See Ann. Sci. Nat. Zool. 5 Ser. vol. viii. 1867. 



Qammarus pulex. Mr. H. Giglioli, who discovered this species, says that he has never found it 

 anywhere else; and that out of 700 Gammari from different localities, not one was free from the para- 

 site. Quart. J. Micr. Sci. N. Ser. vol. iii. 1863, p. 237 



