No. 6.] AMERICAN MORPHOLOGICAL SOCIETY. 351 



at first Macruran, attains the Eupagurid structural plan before 

 the moult to the sixth stage occurs. 



The duration of the glaucothoe stage is dependent on the 

 time of entering the shell. Specimens which take the shell 

 within the first twenty-four hours after the moult from the 

 fourth zoe'a, spend only four or more often Jive days in the 

 stage. A delay of four days before the shell is taken pro- 

 longs this period to six or, in a few cases, to seven days. In 

 fifty glaucothoe kept without any shells, some remained in the 

 stage the minimum four days, but the majority remained six 

 and seven days, and one remained eight days. 



The sixth and following stages introduce no important 

 changes in structure, except the branching of the liver. In 

 this branching, however, the majority of the diverticula of the 

 right lobe go to the right under the intestine, so that this lobe, 

 in the adult, apparently lies on this, its own side, of the intes- 

 tine. The lesser lobes branch later and finally form a small 

 tuft of tubules on each side of the stomach. 



XVII. ESSENTIAL FACTORS IN THE REGEN- 

 ERATION OF PLANARIA MACULATA. 



CHARLES RUSSELL BARDEEX. 



REGENERATION of a new whole individual from a small piece 

 of a parent individual depends in Planaria rnaculata upon 

 the presence in the piece of a part of the central nervous system 

 and a part of the intestinal system. A small piece containing 

 these parts will regenerate from them new typical intestinal and 

 nervous systems. At the same time the parenchyma in the 

 vicinity of the cut surface becomes increased in amount, and is 

 symmetrically differentiated in relation to the new intestinal 

 system. A head may thus be formed anterior to a new axial gut, 

 and lateral and tail areas may be restored. Polarity of the piece 

 is determined by the central nervous apparatus which it contains. 



A new pharynx is formed just posterior to the point where 

 intestinal contents collect when the whole piece contracts. 



