THE AMERICAN LOBSTER. 147 



each other. The pollux is depressed, so that when the claw is closed it falls almost 

 exactly midway between (he normal and first superadded digit. The fission is marked 

 on the upper surface by a distinct groove. The total length of the propodus is about 

 2i inches (62 mm.), so that the lobster was not in all probability over inches long. 

 The size of this claw as compared with the basal joints of the limb suggests that it 

 has been lately regenerated, and it is unfortunate that this interesting point can not 

 be determined with certainty. 



In tig. 196 a similar monstrosity is seen in the dactyl of the Cutting-claw. Here 

 the bifurcating brauch is near the apex. Each prong is furnished with teeth on the 

 inner side. A trimerous dactyl (fig. 195), one division of which is independent, in 

 the second or third pereiopod presents precisely the same relations which occur in the 

 first pereiopod (fig. 193), and probably they have been produced in the same way. 



What is now most needed in clearing up questions in the interpretation of 

 deformities in crustacean appendages is to watch the molting of the animals and to 

 measure and record the change which occurs in the malformed individual at each stage 

 of growth. The abnormal developments seen in figs. 189-193 probably represent a series 

 of changes such as ordinarily occur in the same individual. What the course of events 

 really is between the conditions represented by figs. 193, 192 is not so clear. 



While the true duplication, or even triplication, of limbs or parts of limbs is rare 

 in Crustacea, it is occasionally met with; but it is an important fact, which Bateson 

 has emphasized, that "in arthropods and vertebrates such a phenomenon as the 

 representation of one of the appendages by two identical appendages standing in 

 succession is unknown. No right arm is ever succeeded on the same side of the body 

 by another arm properly formed as a right, and no crustacean has two right legs iu 

 succession where one should be." 1 



In the American Museum of Natural History, iu New York, there is a specimen 

 of a lobster iu which the right cutting-claw is perfectly duplicated from the carpus 

 or fifth joint. I was recently enabled to examine this interesting specimen and to 

 make some drawings of it, which are given in cuts 16, 17, plate E. 



The two cutting-claws resemble each other very closely in every detail and are 

 of almost exactly the same size, but each is relatively smaller than normal. The 

 measurements of each cutting-claw are as follows : 



Right cutting-claws (abnormal) : Inches. 



Length of propocti 3| 



Greatest breadth of propodi If 



Left crushing-claw (normal) : 



Length of propodus 5 



Greatest breadth of propodus 2 



In the primary cutting-claw the dactyl closes normally on the propodus; iu the 

 superadded claw (8. G.) it is bent upward out of line with the cutting edge of the 

 latter. The symmetry of the two claws extends, with few exceptions, to the spines 

 upon their cuttiug edges and on the inner margins of the propodi. The carpus of 

 the limb is apparently single, but it has duplicated spines, and a deep groove at its 

 peripheral end shows that it is virtually double. The carpus and meros have been 

 twisted through an angle of 90°, so that their posterior surfaces face upward. 



This specimen was obtained some years ago from a marketman in New York City. 



'Materials for the study of variation, p. 539. 



