264 BULLETIN OF THE 



claw. The amputated part was evidently removed when the shell was 

 soft, and the wound has completely healed. The dactylus has the form 

 of a cylindrical stunted segment, with an imperfectly developed line of 

 teeth on its cutting surface. The character of the shell leads me to 

 helieve that the amputation passed through the line indicated by x, and 

 that the part of the hand distal to this, as well as the dactylus, was re- 

 produced by budding after the wound was received. 



Although as early as 1671 the fanciful Yon Berniz (No. 1) described 

 and figured two misshapen Crustacean claws, the number of deformities 

 among animals of this class recorded by naturalists is small compared 

 with those observed in insects. Of the thirty cases which I find hith- 

 erto recorded, fifteen belong to the European crayfish (Astacus fluviati- 

 lis).* Leaving out of account the claw represented by Fig. 3 on Plate 

 II., in which we have a simple distortion arising from an abnormal 

 curvature of the fingers, it appears that all the deformities just de- 

 scribed belong to the two categories of monstrositates per defectum and 

 monstrositates per accessum. The former (such as Plate II. figs. 7, 9) 

 are without doubt the result of an accidental amputation of certain 

 parts when the animal was soft-shelled, which parts would probably 

 have been restored after subsequent moults if the animal had lived. 

 Such deformities can hardly be termed true monstrosities, and are of 

 minor interest. The latter, — in which category all the other cases 

 figured will be included, — while accompanied in most cases by a dis- 

 tortion of normal structures, and probably for the most part the result 

 of injuries, present irregular, secondary outgrowths, and are of consider- 

 able interest. Among these we have, first, cases of duplication of joints 

 in a limb (as in Plate I. figs. 12, 13, 16, Plate II. fig. 6), similar to the 

 many cases described among insects ; secondly, processes budding out from 

 either the propodus (Plate I. figs. 9, 11, 14, 17) or the dactylus (Plate I. 

 figs. 1-8, 15, Plate II. figs. 1, 4, 5) without any articulation. These 

 processes frequently simulate a true claw in a marvellous manner, e. g. 

 Plate I. figs. 1-5, and are worthy of especial attention. A Crustacean claw 

 is, morphologically viewed, a composite structure involving two segments 

 of the series of seven which are found in the typical leg. The ultimate seg- 

 ment of the series develops teeth along its inner border, and when flexed 

 closes against an immovable toothed process from the penultimate seg- 

 ment. But in these fictitious claws (see Plate I. figs. 2, 5, etc.) the two 



* It is remarkable that in the vast number of American crayfishes examined by 

 Hagen in the preparation of his Monograph of the North American Astacidcc, no 

 deformities, strictly speaking (seep. 269), were observed. 



