1890.] ON ABNORMAL REPETITION OF PARTS IN ANIMALS. 579 



ordinary prolongation of the azj'gos cardinal vein, though the vena 

 cava was quite of the normal size. 



It will be observed that the continuity between the inter-renal 

 portion of the vena cava and the azygos is quite in accord with the 

 discoveries of Hochstetter^ in the development of these veins. 

 Contrary to the generally received opinion (<■/. for example the dia- 

 gram illustrating the origin of these veins in Wiedersheim's ' Grun- 

 driss der vergleichenden Anatomic der Wirbelthiere,' Jena, 1888, 

 p. 329), Hochstetter found in the Rabbit and the Pig that the vena 

 cava from where it receives the renal veins to a point behind the 

 opening of the ilio-lumbar veins is formed from the right cardinal. 



11. On some Cases of Abnormal Repetition of Parts in 

 Animals. By William Bateson, M.A., Fellow of St. 

 John's College, Cambridge, and Balfour Student in the 

 University. 



[Received June 17, 1890.] 



This paper contains descriptions of some instances of variations 

 consisting in abnormal repetitions of normal structures. A large 

 number of similar or identical facts have already been recorded by 

 many observers, yet every additional record is valuable ; for the 

 significance of a variation depends not only on the form which it 

 takes, but also on the frequency and the degree of completeness 

 with which it takes that form. 



Though one is naturally tempted to draw seemingly obvious de- 

 ductions from the facts about to be given, it is not proposed on the 

 present occasion to do more than describe the actual structures as 

 they are found. For while it is clear that the kej- to some of the 

 problems of variation is to be sought by an analysis of this class of 

 facts, yet such an analysis can only be attempted after a wide survey 

 of the whole ground, and when it shall be possible to bring forward 

 a large collection of the evidence bearing on the subject. I have 

 been for some time engaged in preparing such a collection, and I 

 hope before long to find an opportunity of putting it in order with 

 a view to a full discussion of the modes of variation of Multiple 

 Parts. In the meantime it is best to describe the forms without 

 comment. 



I. — Crah (Cancer pagurus) having the Endopodite of the Third 

 Ala.villipede represented by a Chela. 



This animal was brought by a fisherman to the Laboratory of the 

 Marine i3iological Association at Plymouth. It is a male, measuring 

 five inches from one side of the carapace to the other. All the 



' " TJeber die Bildung der hinteren Hohlvene bei den Saiigethieren," Anat. 

 Anz. Bd. ii. p. .517. 



