532 



MERISTIC VARIATION. 



[part I. 



The various simple forms taken are illustrated by the eight 

 cases shewn in Figs. 184, 185 and 186. It will be seen that when 

 such extra processes arise on the toothed border of the dactylo- 

 podite they turn their smooth borders to each other, but when 



819 



Fig. 186. Homarus americanus. Three chela whose dactylopodites bear double 

 extra dactylopodites. I. A left. II. A left. III. A right. R, normal right. 

 L, normal left. R', extra right. L\ extra left. (From Faxon.) 



they arise on the smooth border they turn their toothed borders 

 to each other, thus fulfilling the conditions of the Scheme given 

 at p. 481. Though from the close agreement between the three 

 prongs in some of the specimens it is not always possible to 

 tell the normal dactylopodite with certainty, it will be seen that 

 in these the rules hold whichever of the two possible prongs be 

 supposed to be the normal. 



Astacus leptodactylus : left chela has dactylopodite as 

 shewn in Fig 187, II. Presumably D is the normal pushed out 

 of place, and D' and D" are the two extra dactylopodites. They 

 are so placed that none meets the index. Karoli, J., Term. 

 Filzetek, 1877, i. p. 53, PI. II. 



