416 



MERISTIC VARIATION. 



[part I. 



is 3, in Blattodea, Mantodea and Phasmodea 5, in Acridiodea 3, 

 in Locustodea 4, in Gryllodea 2 or 3 1 . 



The fact, originally observed by Brisout de Barneville 2 , 

 that in various species of Blattidse the number of tarsal joints 

 may vary from five to four is therefore of considerable importance 

 in a consideration of the manner in which these several forms 

 have been evolved from each other. The species in which Brisout 

 observed this variation were ten in number and belonged to four 

 genera of Blattidse. 



At my suggestion Mr H. H. Brindley has made an extended 

 investigation of the matter and a preliminary account of the 

 results arrived at was given in the Introduction (p. 63). It was 

 found that of Blatta americana 25°/ of adults have one or 



n 



Fig. 125. I. Normal five-jointed left tarsus of Blatta americana. II. Right 

 tarsus of the same having four joints. 



more tarsi 4-jointed. In Blatta orientalis these cases amounted 

 to 15°/ > an d of 102 B. germanica examined, 16 had one or more 

 4-jointed tarsi. 



The abnormality occurred sometimes in one leg and sometimes in 

 another, being more frequent in the legs of the second pair than in those 

 of the first, and much more frequent in the third pair than in either. 

 In some specimens legs of the two sides were symmetrically affected, 

 but this was exceptional. Only one specimen has hitherto been met 

 with having all the tarsi 4-jointed. There was a slightly greater 

 frequency in females than in males. 



When the examination of these abnormal tarsi was begun it was 

 supposed that the variation was congenital, but as explained in a note 

 to the Introduction (p. 65) doubt subsequently arose as to this. It is 

 well known that Blattidse like many other Orthoptera have the power 

 of renewing the appendages after loss, and Mr Brindley found by 

 experiment that when the tarsus of Blatta orientalis is renewed after 

 mutilation the resulting tarsus is 4-jointed. It was also found that 

 4-jointed tarsi were much more frequent in adults than in the young. 

 The question therefore arises, is the 4-jointed tarsus ever congenital 1 



1 From Beunner von Wattenwtl, Prodr. enrop. Orthop., 1882. 



2 Ann. ent. soc. France, s. 2, vi. 1848, Bull., j>. xix. 



