168 



EMBRYOLOGY 



this figure (Fig. 80) has a different orientation from that of the other 

 turbellarian larvre, in order to bring out better its resemblance to the 

 piHdium larva. Its discoverer, Goette, also compares it directly to the 



pilidium. If we consider that Stijlo- 

 cliits has a simijler course of deve- 

 lopment (see supra, the absence of 

 nutritive yolk), then it appears not 

 imjjossible that the larva of St!/loc]ius 

 represents a i^rimitive condition, a 

 lower larval form, which perhaps still 

 has relationships to the larval forms 

 of the Nemerteaiis. The fact that 

 Müllek's larva also i^resents a similar 

 form at a certain stage is an argument 

 in support of this view. Muller's 

 larva itself would then represent a 

 more highly developed form. Lang, 

 to be sure, believes that Stijlochus 

 simply leaves the egg at an earlier 

 stage, arriving at the condition of 

 Muller's larva only during its free 

 existence, whereas Goette maintains 

 that it is developed directly into the 

 adult animal by an increase in length. 



The larva of StijlocJiopsis ponticus described by Metschnikoff ' also 



Fig. 79.— Larva of Oligocladus 

 auriius, Lang {Eunjlepta auriculata. 

 Clap.), seen from the side (after 

 Hallez, from Balfoub's Compara- 

 tive Emhryology). 



\\Mil)'7/^ 



E„r- 



Pig. 80. — Larva of Sti/Jot/ms pJidiinn seen from the side (after Goette). D, in- 

 testine ; En, remains of the entoderm cells; S, pharynx. 



1 This work by Metschnikoff, published in a Kussian periodical,— 

 " Studies on the Development of the Planariaj," Memoirs of the Neo- 



