CHAPTER VII. 



PLATYELMINTHES '. 



TURBELLARIA. 



ALTHOUGH there is perhaps no group in the animal kingdom 

 the ontogeny of which would better repay a thorough investiga- 

 gation than the Turbellarians, yet the difficulties to be overcome 

 have hitherto proved too great. 



The fresh-water Rhabdoccela and Dendroccela do not under- 

 go any metamorphosis, and leave the ovum in a condition in 

 which they cannot easily be distinguished in their general appear- 

 ance from Infusoria. Many marine Dendroccela also develop 

 directly, while, as was first shewn by Joh. Miiller, other marine 

 Dendroccela undergo a more or less complicated metamorphosis. 



Marine Dendroccela. Of the marine Dendroccela which do 

 not undergo a metamorphosis the form most fully worked out is 

 Leptoplana tremellaris (vide Keferstein, No. 187, and Hallez, 

 No. 185). 



The ova are surrounded by large albuminous capsules 

 secreted by a special gland. They are laid a great number at a 



1 I. Turbellaria. 



1 . Dendroccela. 



2. Rhabdocoela. 



II. Nemertea. 



1. Anopla. 



2. Enopla. 



III. Trematoda. 



i. Distomeae. 

 i. Polystomeae. 



iv. Cestoda. 



