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



277 



After extending slowly down the column for a varying period 

 of days, under the perisarc, the frustule develops a clavate tip 

 and dissolves a passage through the latter by means of the eel lis 

 with which the ectoderm is now furnished. The clavate end is 

 capable of secreting perisarc also. It behaves in these respects 



Fig. 23. 



Longitudinal section through developing frustule of adult. Endo- 

 derm ruptured at base of frustule. 



like the end of a stolon, and in one other : it is amoeboid. I have 

 described elsewhere its locomotion,^ which has an intimate bear- 

 ing on the future form of the organ. The stimulus of contact, 

 though in no sense a cause of the origin of the frustules, is an 



Fig. 24. Section similar to last, very slightly oblique. 



important factor in their development. Their club-shaped ends 

 flatten when they reach a substratum and suddenly begin active 

 creeping movements which have been observed to carry them 

 ° Journal of Experimental Zoology, I, p. 416. 



