PL A TYELMINTIIES. \ 5 9 



The body is somewhat oval, and slightly pointed behind. At the 

 anterior end are placed the eyes, two in the youngest larva of Miiller, 

 and twelve in the older larva (fig. 88), and in the middle of the 

 ventral surface is the mouth. It is surrounded by a strong fold, and 

 leads into an alimentary canal, which is at first simple, but in the 

 older larvae is much branched. A bilobed ganglion connected with 

 two nerve cords is placed anteriorly. The superficial epithelium is 

 ciliated, and below it is a layer of cells (cutis) derived from the 

 primitive epiblast, in which are formed the usual rods (Hallez). 

 The chief peculiarity of the larva consists in the presence of elongated 

 processes covered with long cilia, and so connected together by a ciliated 

 band that the whole together forms, in Miiller's larva at any rate, 

 a lobed prworal ciliated band (fig. 88). This band is not quite so clear 

 in Hallez' figures. Miiller's youngest larva was provided with eight 

 very long lobes ; three were dorsal, viz. a median anterior, and two 

 lateral placed far back ; three ventral, viz. a median in the front of 

 the mouth forming a large upper lip, and two processes at the sides of 

 the mouth. The number was completed by 

 two lateral processes of the body. All the 

 processes except the dorsal median one are 

 shewn in fig. 88. In Hallez' larva, fig. 87, 

 the six posterior processes form a rather 

 definite ring, while one flagellum projects 

 from the front end of the body immediately 

 below the eyes, and a second flagellum behind. 

 In Moseley's youngest larva six processes 

 only were present, though subsequently eight 

 became formed as in Miiller's larvae. 



The metamorphosis consists in the whole 

 animal growing longer and flatter, and in the F IG . $8. MULLEK'S TOR- 

 arms becoming gradually shorter and shorter BELLARIAN LARVA (PROBABLY 

 till they finally disappear altogether, and the THYSAN ZON). VZEWED 



J . J ,-. l V 1 , ^ FROM THE VENTRAL SURFACE. 



larva acquires the ordinary adult lorm. (After Miiller.) 



The lobed larval form of the Turbellaria The ciliated band is re- 

 has some points of resemblance to the Pili- P resent ed by the black line. 

 ,. r c ,. i j >i j i m. mouth; wJ. upper lip. 



dium form 01 nemertme larva described be- 

 low, yet its resemblance to this interesting larva is less close than would 

 appear to be the case with certain turbellarian larval forms recently 

 described by Gotte and Metschnikoff, which are in some respects 

 intermediate in character between the larva of Leptoplana and those 

 just described. 



The observations of Gotte (No. 184) were made on Planaria Neapoli- 

 tana and Thysaiiozoon Diesingi, and those of Metschiiikotf (No. 188) 

 on Stylochopsis ponticus. The larvae of all these forms undergo more 

 or less of a metamorphosis, but the accounts of their development are 

 not easily reconciled 1 . The early stages of Planaria are like those of 



1 The account of Metschnikoff's observations on Stylochopsis ponticus given in 



