386 
F. M. BALFOUR. 
(fig. 7). The Auricularia, the Bipinnaria, and the Pluteus can be reduced 
to a common type (fig. 18 c). 
Enteropnetjsta. — Tornaria (fig. 16). 
Urochorda (Tunic at a). —The tadpole-like larva. 
Ganoidea. — A larva with adhesive disc with papillae in front of the 
mouth. 
Anurous Amphibia. — The tadpole. 
Of the larval forms included in the above list a certain 
number are clearly 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 do not propose to discuss the significance 
of these forms in the present essay. 
Fig. \.—Two free Stages in the development of Sycandra raphanns. (After 
Schultze.) A. Amphiblastate stage. B. Stage after the ciliated cells 
have commenced to be invaginated. c.s. 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 
conclusions. The infusoriform larva of the Dicyemidge, and 
the Cercaria of the Trematodes are such forms. 
The meaning of the Amphiblastula larva was discussed 
in a previous essay. 
Excluding these and certain other forms, we have finally 
left for consideration the larvae of the Coelenterata, the Tur- 
bellaria, the Rotifera, theNemertea the Mollusca, the Polyzoa, 
the Brachiopoda, the Chaetopoda, the Gephyrea, the Echino- 
dermata, and the Enteropneusta. 
The larvae of these forms can be divided into two groups. 
