444 Mabel Bishop 



or, in other words, they represent four successive stages in the cosmobiotic 

 series which leads through dicephali to the Tocci group, and thence 

 through ischiopagy to duplicate twins [Wilder, 1904, series A and D].* 

 The material studied consists of: — 



1. A normal pig, very young, umbilical cord still attached. [Obtained 



from F. D. Lambert.] 



2. A normal lamb, and a normal turtle (Chrysemmys picta). 



3. Pig fwt us, probably at term, diprosopus triophthalmus ; Teras XII 



of H. H. Wilder's collection. [Obtained from B. G. Wilder.] 



4. Pig embryo 22 mm. long, diprosopus tetrophthalmus ; Teras I of 



H. H. Wilder's collection. [Obtained from F. D. Lambert.] 



5. Bicephalous lamb, three to four weeks old, born at Ludlowville, New 



York; Teras XV of H, H. Wilder's collection. [Obtained from 

 B. G. Wilder.] 



6. Two-headed turtle, Chrysemmys picta, just hatched ; Teras XX of 



H. H. Wilder's collection. [Obtained from A. D. Mead.] 



The last four specimens are listed in the order of their sequence in 

 the cosmobiotic series, the simplest stage first. For the sake of con- 

 venience I shall hereafter refer to these according to the number in 

 Professor Wilder's list, as given above. 



I am directly indebted to Professor Wilder for this material, and 

 indirectly to the gentlemen whose names are bracketed. To all of them 

 I desire to express my thanks for their contributions of material, which 

 have made the present investigation possible. 



Teras XII is a pig foetus delivered at term, perfectly normal in 

 appearance, except in the head region. The length of the animal from 

 the tip of either snout along the mid-dorsal line to root of tail is 36.5 

 cm. (tail — 7.5 cm.). The condition in the head region places the creat- 

 ure at once in that class of anomalies which is more than one but less than 

 two individuals (monstra in excessu), and represents the first stage 

 beyond the normal in the cosmobiotic series already defined. 



For simplicity in this and in the other terata, I shall designate the 

 right head, or portion of head, as "Component A," and the left as 

 "Component B." 



Teras XII resembles closely in external doubling the human diprosopi 

 triophthalmi of Forster [Tafel I, Fig. 1], Ahlfeld [Tafel IX, Fig. 1], 



^Wilder, H. H.. Duplicate Twins and Double Monsters, Amer. Jour, of Anat.» 

 Vol. Ill, 1904. 



