106 LIBBIE H. HYMAN 



gration begins at the anterior end, and proceeds backwards along 

 the axis to the posterior end. This is interpreted to mean that 

 the head, or what represents the head, of the organism is carry- 

 ing on metabohc processes at the highest rate, and that the rate 

 of metaboHsm decreases along the antero-posterior axis. This 

 kind of gradient exists in the egg, and Child ('13 c) has suggested 

 that it is the physiological basis for the law of antero-posterior 

 development. Child further suggests that this gradient, exist- 

 ing in the protoplasm of the egg is carried over to the nervous 

 system when the latter develops. The cephalic end of the nerv^- 

 ous system thus exercises from the very first physiological 

 dominance over the rest of the organism, and retains this domi- 

 nance by virtue of its functional relations to other parts, even 

 though its actual metabolic rate may, and does, fall throughout 

 ontogeny. The gradient of the adult animal may therefore vary 

 markedly from the original gradient; various parts may attain 

 a higher rate of metabolism than the head itself ; but the nervous 

 system, owing to long-established antero-posterior conduction 

 paths, can maintain control, for some time at least, over regions 

 of higher metabolic activity than its own. 



Is the gradient of the adult oligochaete of the primary type? 

 I have found it so in but one species examined, namely, Aeolosoma 

 hemprichii, a member of the most primitive family of oligochaetes. 

 This worm is very small, only 1-2 mm. in length, has a rounded 

 prostomium, a ciliated funnel-shaped pharynx leading into the 

 intestine, and numerous red oil globules in the body wall. 

 Each animal nearly always consists of two or more zooids which 

 arise in connection with fission planes in the typical annelid 

 manner; before they appear morphologically, they are present 

 physiologically, as is readily demonstrated by the cyanide method. 



For the disintegration experiments, a concentration of y^, 

 KCN is used, and the animals are placed in covered watch glasses 

 as already described. In an individual without zooids, the dis- 

 integration begins at the tip of the prostomium and proceeds at 

 first slowly, then more rapidly along the axis. The integumental 

 oil globules remain intact longer than the parts in which they 

 were imbedded, but eventually they vanish by sudden extrusion 



