192 



TURBELLARIA. 



larian, soon assumes a dendritic form. The young animal after these changes 

 resembles its parent, except in the possession of only two pairs of eyes and 

 in the absence of generative organs. 



Of the types with a complete metamorphosis the free larvae 

 of various species of Thysanozoon have been observed by Joh. 

 Miiller (190) and Moseley (189), 

 and the complete development of 

 Eurylepta auriculata has been 

 studied by Hallez. 



The stages within the egg of 

 this latter type agree precisely 

 with those already described in 

 Leptoplana. After the formation 

 of the mouth the body elongates, 

 remaining however cylindrical. A 

 fold forms on the anterior side of 

 the mouth, giving rise to a large 

 upper lip. Two posterior processes 

 are next formed, and other pro- 

 cesses soon arise, constituting the 

 whole of those found in the free 

 larva. The embryo next shakes off its egg membranes by a 

 series of vigorous contractions. When free it has the form repre- 

 sented in the annexed figure (fig. 87). 



It is so similar to Muller's (fig. 88) and Moseley's larvae that 

 all three may be dealt with together. 



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 Muller's larva at any rate, a 



FIG. 87. LARVA OF EURYLEPTA 

 AURICULATA IMMEDIATELY AFTER 

 HATCHING. VIEWED FROM THE 

 SIDE. (After Hallez.) 



m. mouth. 



