MERISTIC VARIATION 



43 



Herringham * dissected to their origin the nerves forming 

 the brachial plexus in fifty-five human subjects (thirty-two fetal 

 and twenty-three adult). Quoting from his work, Bateson says : 



The origin of the ulnar nerve was traced in thirty-two cases, fourteen 

 being adults. It (the ulnar nerve) was found to arise in four different ways. 

 Most commonly it arises from the vinth and ixth ; this occurred in twenty- 

 three cases. With the vinth and ixth is sometimes combined a strand from 

 the vnth, as shown in five cases (four fetal, one adult). In three fetal 

 cases it arose from the vnith only, and in one fetal and one adult case from 

 the vuth and vinth. ... In several cases the branch from the vnith was 

 much larger than that from the ixth, but the reverse was never met with. 



Similar conditions were found elsewhere with man, the gorilla, 

 baboon, and chimpanzee, and the following principle was set 

 forth: " Any given fiber may alter its position relative to the 

 vertebral column, but will maintain its 

 position relative to other fibers.''' 



Homceosis in insects and other small 

 animals. The replacement of one part 

 by another, while common among plants 

 (modified leaves and stems), is compar- 

 atively rare in animal life. It is, however, 

 by no means unknown, and some striking 

 examples are quoted from Bateson to 

 show the remarkable manner in which a 

 perfect part may arise in a most unusual FlG - 4- Homceotic variation 



place, among which are the following : 2 



in sawfly: right antenna 

 normal; left antenna 

 bearing a foot. A and B, 

 enlarged. After Bateson 



1. Specimens of sawfly (Cimbex axillaris} in 

 which the left antenna ended in " a well-formed 



foot, having a pair of normal claws and the plantula between them " 

 (Fig. 4). Right antenna normal. 3 



2. A male bumblebee {Bombus variabilis} taken in Munich showed the 

 left antenna " partially developed as a foot," bearing " a pair of regularly 

 formed claws like the claws of the foot." 



3. A male specimen viZygana filipendulce " possessing a supernumerary 

 wing arising in such a position as to suggest that it replaced a leg" (Fig. 5). 

 The extra wing was on the left side and projected from the underside of the 

 body after the exact fashion of the leg, which was absent. The specimen 



1 Bateson, Materials, etc., pp. 135-138. 2 Ibid. p. 147. 



3 Ibid. pp. 146-155. Professor Bateson vouches for the genuineness of this 

 specimen, which he himself carefully examined, although it belonged to Dr. Kraatz. 



