36 C. M. CHILD. 



3. The high end of the oocyte gradient becomes the apical pole 

 of the egg at maturation and in early cleavage stages. During 

 later cleavage a gradient is continuously present, but absence of 

 landmarks makes complete demonstration of its identity with the 

 gradient of earlier stages impossible, though there is no reason 

 to doubt that it is the same. From the beginning of locomotion 

 on the identity of the gradient is certain, the high end being the 

 apical, the low end, the basal pole of the larva. 



4. As the planula elongates a second gradient opposite in direc- 

 tion to the primary gradient appears at the basal end of the larva 

 and gradually extends toward the apical end. Soon after this 

 gradient appears the planula of PhiaKdiwm and of Gonothyraa. 

 attaches itself by the original apical end and the second gradient 

 becomes the hydranth-stem axis. Attachment of the planula of 

 Stomotoca was not observed. 



5. The origin of this second polarity, opposite in direction to 

 the first, is interpreted as a result of physiological isolation of the 

 basal end of the planula in consequence of increase in length. 

 From this viewpoint the hydranth-stem axis represents a process 

 of budding not essentially different physiologically from other 

 processes of budding in hydroids and various other forms. 



REFERENCES. 



Child, C. M. 



An Analysis of Form Regulation in Tubularia. I. Arch. f. En- 

 twickelungsmech., XXIII. 



An Analysis, etc. IV., V. Arch. f. Entwickelungsmech. XXIV. 

 '15 Individuality in Organisms. Chicago. 



'20 Some Considerations Concerning the Nature and Origin of Physio- 

 logical Gradients. BIOL. BULL., XXXIX. 



'21 The Origin and Development of the Nervous System. Chicago. 

 *23a The Axial Gradients in Hydrozoa. V. BIOL. BULL., XIV. 

 *23b The General Relation Between Susceptibility and Physiologic Con- 

 dition. Arch. Int. Med., XXXII. 



'24 Physiological Foundations of Behavior. New York. 

 Torrey, H. B. 



"07 Biological Studies on Coryinorpha. II. Univ. of Cal. Publ., Zoology. 

 III. 



