154 CHARLES ZELENY. 



The nearest approach to the condition of the present double 

 chela that I have been able to find in the literature is the right 

 cutting chela of a female lobster figured by Herrick on p. 147, 

 plate E, of his "American lobster." This gives a chela which is 

 apparently truly double from the carpopodite out. The two 

 parts resemble each other very closely. 



In Bateson's list 1 Nos. 832 to 835 come under the same head. 

 Of these No. 833 (Fig. 200 I, p. 542) described by Faxon 2 

 as a right chela of Hoinarns americanns shows two dactylopodites 

 articulating separately. The index is bifid at its tip and has two 

 rows of teeth, one on each edge. If the separation of the dacty- 

 lopodites had been slightly greater than shown in Faxon's figure 

 and the split in the index had extended slightly further down on 

 its side than the split in the dactyl a fair representation of the 

 condition in the Gelasimus chela would have resulted. A simi- 

 lar modification in the degree of the split would bring Nos. 832, 

 834 and 835 into the same category. 



There can be no doubt that the present regenerated double 

 chela is a true double appendage, one part being a mirror image 

 of the other except for the slight differences given above. The 

 relation of the parts is such as one would expect if after the 

 regenerating bud of the chela had become specified a mechanical 

 force had partly separated it into two nearly equal parts by a 

 quantitative split, /. e., one passing in the plane of the future 

 chela. With but a slight rearrangement of the materials in the 

 two parts each is supposed to have been able to form a complete 

 pincher in a manner entirely similar to that in the constriction 

 experiments of Spemann and others 3 on Amphibian eggs by 

 which double and partly double embryos were produced. The 

 wider separation of the indices as compared with the dactyls is 

 supposed to be due to the greater depth of the mechanical split 

 on this side. 



I have no suggestion to make as to the nature of the agency 

 which caused the division of the embryonic mass. Spemann's 



1 L. c. t pp. 541, 542. 



2 Faxon, Bull, of the Mits. of Comp. Zobl. ffarv., Vol. VIII., No. 13, 1881. 



3 Spemann, Hans, " Entwickelungsphysiologische Studien am Triton -Ei," Rotix^ 's 

 Archiv, Bd. XII., p. 224, 1901. Herlitzka, A., Roux" s Archiv, Bd. II., pp. 

 352 ffl. Endres, H., Rottx's Archiv, Bd. II., pp. 517 ffl. 



