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wounds the whole limb is usually autotomised, while in distal injuries the limbs are quite frequently retained and the lost parts restored by regeneration,-it follows that if abnormal structures do arise as the result of the injury of normal and regenerating buds, it would be most natural to expect that such abnormal structures would be most frequently found on the distal segments. In our examination of Faxon's and Bateson's lists, we have found that this is exactly the

case.

Taking into account, then, these relations between the nature of the injury, autotomy, and regeneration, it appears, therefore, that the fact that the great majority of crustacean deformities occur on the distal segments of the limb readily lends itself to the interpretation that they are the result of regenerative processes.

3. The Regeneration of Extra Legs Following an Artificial Splitting of Nerves.

3. A third point of importance is the effect of injuries which involve a division of the nerve. Miss Reed ('04) in her study of regeneration mentions certian results which she obtained in the hermit crab by splitting the stump of the leg lengthwise after autotomy had taken place. "In several cases after splitting the stump, two extra legs appeared in a short while. Sections through this region show that the nerve is split, one branch going to each leg. It is probable that a new leg was developed at each end of the split nerve, since in all other cases where only one leg regenerated the nerve shows no sign of any injury. In this case it is probable that the nerve was not cut" (p. 315). Unfortunately, Miss Reed has not described these regenerated extra legs, but this result is certainly very suggestive; it not only furnishes further evidence for the origin of extra structures through regenerative processes, but also indicates an important method for future experiments. In view of these results one is also tempted to ask whether the rare case of triple legs recorded by Bateson for the European lobster (No. 808) may not have arisen through an accidental fracture of the nerve stump and a consequent triple regeneration.

In the conclusion of this study of abnormal structures, therefore, we may say that sufficient evidence has now been adduced to prove that both abnormal symmetrical and duplicated appendages among curstacea do arise through the process of regeneration. And the experimental results so far attained indicate that we may yet be able to control the formation of these abnormalities by proper mutilation, and thus open up for experimental study an important field of organic variation.

• LITERATURE CITED.

ANDREWS, E. A., '04-"An Aberrant Limb in the Crayfish." Biol. Bull., Vol. VI, No. 2, pp. 75-83.

BATESON, W., '94-"Materials for the Study of Variation." London, 1894.

CALMAN, W. T., '06-"Exhibition of a Photograph of a Lobster with Abnormal Chele." Proceed. of the Zoöl. Soc. of London, p. 633.

EMMEL, V. E., '05-"The Regeneration of Lost Parts in the Lobster." Thirty-fifth Annual Report of the Rhode Island Commission of Inland Fisheries, pp. 81-117. Special paper, No. 20.

EMMEL, V. E., '06-"The Relation of Regeneration to the Molting Process of the Lobster." Thirty-sixth Annual Report of the Rhode Island Commission of Inland Fisheries, pp. 257-313; Special paper, No. 27.

EMMEL, V. E., '06-(a) "Torsion and Other Transitional Phenomena in the Regeneration of the Cheliped of the Lobster." Journal of Exp. Zoology, Vol. III, No. 4, pp.603-618.

EMMEL, V. E., '06-(b) "The Regeneration of Two 'Crusher-claws' following the Amputation of the Normal Asymmetrical Chelæ of the Lobster (Homarus Americanus)." Archiv. f. EntwMech., Bd. XXII, pp. 542-552.

EMMEL, V. E., '07-"Regeneration and the Question of 'Symmetry in the Big Claws of the Lobster.'" Science, 1907, (now in press). FAXON, W., '81-"On Some Crustacean Deformities." Bull. of the

Mus. of Comp. Zoöl., Harvard, Vol. VIII, No. 13, 1881. HADLEY, P. B., '05-"Changes in Form and Color in Successive Stages of the American Lobster." Thirty-fifth Annual Report of the Rhode Island Commission of Inland Fisheries, pp. 44-80. Special paper, No. 19.

HERRICK, F. H., '95-"The American Lobster." Bull. U. S. Fish Commission, 1895.

HERRICK, F. H., '05-"The 'Great Forceps' of the Lobster." Science,

N. S., Vol. XXI, p. 375.

MORGAN, T. H., '04-"Notes on Regeneration." Biol. Bull., Vol. VI, pp. 159-172.

PRZIBRAM, H., '01-"Experimentelle Studien über Regeneration. I." Archiv. f. Entw.-Mech., Bd. XI, pp. 321–345.

PRZIBRAM, H., '02-"Experimentelle Studien über Regeneration. II." Archiv. f. Entw.-Mech., Bd. XIX, pp. 181-247. PRZIBRAM, H., '05-“Die ‘Heterochetie' bei decapoden Crustacean, III." Archiv. f. Entw.-Mech., Bd. XIX, pp. 507-527.

REED, MARGARET A., '04-"The Regeneration of the First Leg of the
Crayfish." Archiv. f. Entw.-Mech., XVIII, p. 307.

STAHR, H., '98-"Neue Beiträge zur Morphologie der Hummer-
schere." Jenaische zeitschr. f. Naturw., Bd. XXXII, p. 475.
WILSON, E. B., '03-"Notes on the Reversal of Asymmetry in the
Regeneration of the Chela in Alpheus heterochelis."
Bull., Vol. 4, p. 197.

Biol.

ZELENY, C., '05-"Compensatory Regulation." Journ. of Exp. Zoology, Vol. 2, p. 197.

ZELENY, C., '05-(a) "The Regeneration of a Double Chela in the Fiddler Crab (Gelasimus Pugilator) in Place of a Normal Single One. Biol. Bull., Vol. 9, p. 152.

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D'(R+L). Abnormal processes interpreted as being morphologically double

[blocks in formation]

1. 2.

The two parts of the extra bud shown in Figs. 10-14.

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PLATE I.

Fig. 1 (Page 103). -Crusher claw of left chela with two extra processes (D'R', D'L') on the outer or smooth border of the normal dactyl. ( x natural size.)

Fig. 2 (Page 104).-Nipper claw of left chela with an extra process D'(R'+L') on the inner
or toothed border of dactyl. (x.)

Fig. 3 (Page 105).-L.eft chela with two extra dactyls (D'R', D'L'), and an extra double
index, I'(R+L). (x.)

Fig. 4 (Page 107). -Nipper claw on right chela with two extra indices (I'L', I'R') and the NIV

OF

stump of a double extra dactyl (?). D'(R+L). (x.)

MICH

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