Vol. 3] Torrey. — Biological Studies on Corymorplia. 



259 



extremity, as with the plannla ; the end which remains in contact 

 with the snbstratnm l)e('omes the aboral extremity and in so far 

 corresponds with the anterior end of the free plannla. 



1. Locomotion. — In leaving the chitinous egg capsule, the larva 

 follows the course of the young growing stem. The wall at the 

 point of exit is dissolved (Fig. 7), and the larva, as it emerges 

 (Fig. 8), secretes a thin layer of perisarc which completely in- 



Fig. 7. Embryos emerging form the egg case, at different angles with 

 the vertical. Prom above. X 116. 



vests it and is continuous with the egg capsule. Unlike the 

 ordinary growing stem, however, it exhibits a tendency for loco- 

 motion which is seen only under exceptional circumstances in 

 permanently attached hydroids. 

 Locomotion is accomplished by 

 means of amoeboid cells in the ec- 

 toderm, and is always away from, 

 never toward the egg capsule. A 

 thin collapsed tube of perisarc is 

 left behind. 



2. Polarity. — From the moment 

 the larva begins to emerge from 

 its egg capsule, oral end foremost, 

 it may be said to possess a definite 

 polarity. Elongation takes place 

 along an axis which does not ap- 

 ^ear to coincide with the longer 

 egg axis, nor with any other rec- 

 ognizable axis preexisting in the egg. If any such relation 

 exists, it is probably readily obliterated by the reaction to 



Fig. 8. Embryo half out of 

 egg case, enveloped iu perisarc. 

 X 116. 



