chap, xxiv.] AXIAL DUPLICITY: REPTILES. 561 



is sometimes supposed that axial duplicity is a phenomenon more 

 or less peculiar to Man and to domesticated animals [and plants], 

 and the occurrence is looked on as a part of that Meristic in- 

 stability which is ascribed to absence of the control of a strict 

 and Natural Selection. This view is far from sound. Such 

 phenomena have on the contrary been found in many classes of 

 animals, vertebrate and invertebrate, and the unquestionable 

 frequency in domesticated animals may in great measure be 

 fairly attributed to the comparative ease with which the births 

 of these creatures can be observed. As considerations of this 

 kind have weight with many it has seemed worth while to give 

 references to examples taken from a variety of different groups, 

 shewing not only that such compound bodies may be produced 

 in wild animals, but also that they may sometimes be able to carry 

 on the business of life without artificial help. 



In Mammals and Birds I do not know an authentic case of a double 

 monster that had grown uj) in the wild state. 



In Reptiles many such cases are known and are referred to by 

 most of the older writers. Of Snakes having complete or partial 

 duplicity, nearly always of the head, some twenty cases are recorded. 

 Several of these were animals of good size, and must have had an 

 independent existence for some considerable time. 



Some of the cases have special points of interest, but into these it 

 is not now proposed to enter. As bearing on the question of the 

 frequency of Meristic Variation in families and strains attention is 

 called to the circumstance that Mitchill's three specimens were all 

 found in one brood of 120 which were taken with the mother. The 

 following is a list of records of snakes having the head wholly or 

 partially double. 



Coluber constrictor. Wyman, J., Proc. Bost. N. H. S., 1862, 

 ix. p. 193, fig. 



Coluber constrictor. Mitchill, S. L., Amer. Jour, of Sci, x. 

 1826, p. 48, PI. (3 specimens). 



Ophibolus getulus. Yarrow, Amer. Nat., 1878, xn. p, 470. 



Pityophis. ibid., p. 264. 



Pelamis bicolor. [Remarkable case 1 : the duplicity appearing 

 only in the fact that there were 4 nasal plates instead of 2, each with a 

 nostril] Boettger, 0., Bar. lib. d. Seuck. nat. Ges. in Frank/, a. M., 

 1890, p. lxxiii. 



In the remainder the species is not clear. Redi, Osserv. int. agli 

 anim. viventi, &c, 1778, p. 2, Tav. I. [very good account]; Lacepede, 

 Hist. nat. des Sevens, n. 1789, p. 482; Bancroft, Nat. Hist, of 

 Guiana, 1769, p. 214, PI. ; Lanzoni, Miscell. curios., 1690, Obs. clxxi. 

 p. 318, Fig. 36 ; Boston Soc. Med. Imp., Catal. of Mus., No. 856, 

 quoted from Wyman, I. c. ; Edwards, Nat. Hist, of Birds, &c, Pt. iv. 

 1751, p. 207, PI. ; Dorner, Zool. Gart., 1873, xiv. p. 407; Coll. Surg. 

 Mus., Terat. Cat., 1872, Nos. 24—27. 



1 Compare with Mitchill's two last cases, and also with a case in Alytes ob- 

 stetricans. Heeon-Koyeb, Bull. Soc. Zool. France, 1884, ix. p. 164. 



B. 36 



