10 PLATYHELMINTHES TURBELLARIA chap. 



Leptoplana employs two kinds of movement, creeping and 

 swimming. Creeping is a uniform gliding movement, caused 

 by the cilia of the ventral surface, aided perhaps by the longi- 

 tudinal muscular layers of this surface, and is effected on the 

 under side of the " surface-film " of water almost as well as on a 

 solid substratum. Swimming is a more rapid and elegant move- 

 ment, employed when alarmed or in pursuit of prey. The 

 expanded fore-parts of the body act as lobes, which are flapped 

 rapidly up over the body and then down beneath it, undulations 

 running rapidly down them from before backwards. The action 

 in fact is somewhat similar to that by which a skate swims, 

 a resemblance pointed out long ago by Duges 1 (Fig. 3). 



We have few direct observations on the nature of the food of 

 Leptoplana, or the exact mode by which it is obtained. Dalyell, 2 

 who observed this species very carefully, noticed that it was 

 nocturnal and fed upon a Nereis, becoming greatly distended 

 and of a green colour after the meal, but pale after a long fast. 

 Keferstein 3 noticed a specimen in the act of devouring a 

 Lumhriconereis longer than itself, and also found the radulae of 

 Chiton and Taenioglossate Molluscs in the intestine. That such 

 an apparently weak and defenceless animal does overpower large 

 and healthy Annelids and Mollusca, has not hitherto been 

 definitely proved. Weak or diseased examples may be chiefly 

 selected. The flexible Leptoplana adheres firmly to its prey, and 

 the rapid action of the salivary glands of its mobile pharynx 

 quickly softens and disintegrates the internal parts of the victim. 

 The food passes into the stomach (Fig. 2, nag), and is there 

 digested. It is then transferred to the lateral branches of the 

 intestine, and, after all the nutritious matters have been absorbed, 

 the faeces are ejected with a sudden contraction of the whole 

 body through the pharynx into the water. 



Leptoplana probably does not live more than a year. In the 

 spring or summer, batches of eggs are laid and fixed to algae or 

 stones by one individual, after having been fertilised by another. 

 Young Leptoplana hatch out in two to three weeks, and lead a 



1 Ann. Sci. Nat. 1 ser. torn. xv. 1828, p. 146. "La Planaire tremellaire . . . 

 peut parcourir ... en faisant battre rapidement ses parties laterales a la maniere 

 des larges nageoires des Raies." 



2 Observations on Planariac. Edinburgh, 1813, p. 12. 



3 "Zur Anat. u. Entwickl. einiger Seeplanarien v. St. Malo," Abli. K. Gesell- 

 sehaft d. JViss. Gottingen, 1868. 



