1898.] APPENBAGES IN THE ARTHROPODA. 945 



to say that just as appendages reproduced like the normal are true 

 to a type, so those which differ from the normal are true to a type 

 also, and are not merely irregular and unfinished imitations of the 

 normal structures concerning which it is possible to say " this is 

 the normal structure with such and such a part wanting or mal- 

 formed." The features leading to the above conclusion are briefly 

 as follows : — 



The most prominent is that the number of joints is less than 

 the normal. This numerical difference is, with certain rare 

 exceptions, an actual one and not merely an apparent difference 

 due to such a factor as the presence of incompletely formed articu- 

 lations. The joints of the appendage are distinctly marked off 

 from each other by articulations of apparently normal completeness. 

 Another character is that in cases where the normal appendage 

 possesses the terminal joint or joints differentiated from the others 

 in length or form, the reproduction has its terminal joint or joints 

 modified so as to in some cases apparently exactly, and in others 

 to approximately resemble those of the normal. 



A third character is that the special features are perpetuated 

 through all stadia into maturity, no matter what instar suffered 

 the loss necessitating reproduction. The evidence as to this is, 

 however, not complete in all cases, but there is no record of 

 numerical increase taking place in a reproduced appendage. 

 That this is so is of interest in connection with the fact that in cases 

 where the normal post-embryonic development is prolonged it is 

 characteristic that the number of joints in at least the case of 

 antennae is progressively increased. At present the evidence 

 suggests that the growth reproducing a lost appendage is without 

 the power of numerical increase. If this is really so, it is necessary 

 to ask whether we are justified in regarding the phenomena of 

 reproduction as equivalent to a simple recurrence of normal develop- 

 ment in at all e\ents such cases as those under consideration. In 

 the instance of the reproduced tail of Lizards we know that it is 

 not. If the regeneration of a Tracheate limb is a process of 

 budding, there is at least one difference between a congenital and 

 a reproduced limb — viz., that the former arises as an outgrowth 

 from the trunk, while the latter is a product of the basal part of 

 the limb itself and so is not a regrowth of the entire limb. If, 

 on the other hand, ecdysis involves reconstruction of the soft 

 parts, the regeneration of a lost appendage must be brought about 

 by changes more like those which usher in each successive stadium 

 under normal circumstances. 



It has been suggested from time to time that such departures 

 from the normal as have been described above should be regarded 

 as equivalent to normal appendages with one or more joints omitted, 

 and sometimes it has been sought to identify particular joints of 

 the normal as absent in the reproduced limb ; but these suggestions 

 have rested on the general appearance of the latter and not on 

 statistical comparisons of the features of the normal and reproduced 

 structures. 



