PLATYELMINTHES. 



193 



lobed pr&oral ciliated band (fig. 88). This band is not quite so 

 clear in Hallez' figures. Muller'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 com- 

 pleted 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 pro- 

 cesses only were present, though subse- 

 quently eight became formed as in Muller's 

 larvae. 



The metamorphosis consists in the 

 whole animal growing longer and flatter, 

 and in the arms becoming gradually 

 shorter and shorter till they finally dis- 

 appear altogether, and the larva acquires 

 the ordinary adult form. 



The lobed larval form of the Turbellaria has some points of 

 resemblance to the Pilidium form of nemertine larva described 

 below, 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 Neapolitana 

 and Thysanozoon Diesingi, and those of Metschnikoff (No. 188) on Stylo- 

 chopsis 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 Leptoplana, as 



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

 the German abstract is too obscure to be placed in the text, but the following are the 

 more important points which can be gleaned from it. 



The ovum becomes first divided into eight segments. By further division along 

 the equatorial zone, a ring of small cells is formed which becomes the epiblast. The 



B. II. 13 



FIG. 88. MULLER'S TUR- 

 BELLARIAN LARVA (PRO- 

 BABLY THYSANOZOON). 

 VIEWED FROM THE VEN- 

 TRAL SURFACE. (After 

 Mullen) 



The ciliated band is re- 

 presented by the black line. 



HI. mouth ; it./, upper 

 lip. 



