302 



TYPES OF LARV.E. 



EcHiNODEBMATA. — The Auricularia (fig. 223 a), the Bipinnaria (fig. 223 b), and the 

 Pluteus (fig. 224), and the transversely-ringed larvae of Crinoidea (vol. i. fig. 268). The 

 three first of which can be reduced to a common type (fig. 231 c). 



Enteropneusta. — Tornaria (fig. 229). 



Urochobda (Tunicata). — The tadpole- like larva (vol. ii. fig. 8). 



Ganoidei. — A larva with a disc with adhesive papillae in front of the mouth (vol. ii. 

 fig. 67). 



Anubous Amphibia. — The tadpole (vol. ii. fig. 80). 



Of the larval forms included in the above list a certain number 

 are probably without affinities outside the group to which they 

 belong. This is the case with the larvae of the Myriapoda, the 

 Crustacean larvae, and with the larval forms of the Chordata. I 

 shall leave these forms out of consideration. 



Fig. 215. Two free stages in the development of Sycandra raphanus. 

 (After Schultze.) 



A. Amphiblastula stage. 



B. Stage after the ciliated cells have commenced to be invaginated. 



C.8. segmentation cavity; ec. granular epiblast cells ; en. ciliated hypoblast cells. 



There are, again, some larval forms which may possibly turn out 

 hereafter to be of importance, but from which, in the present state of 

 our knowledge, we cannot draw any conclu.sions. The infusoriform 

 larva of the Dicyemidai, and the Cercaria of the Trematodes, are such 

 forms. 



Excluding these and certain other forms, we have finally left for 

 consideration the larvae of the Ccelenterata, the Turbellaria, the 

 Rotifera, the Nemertea, the Mollusca, the Polyzoa, the Brachiopoda, 

 the Chaetopoda, the Gephyrea, the Echinodermata, and the Entero- 

 pneusta. 



The larvae of these forms can be divided into two groups. The 

 one group contains the larva of the Ccelenterata or Planula, the other 

 group the larvae of all the other forms. 



