534 E. KAY LANFCESTEll. 



manifest itself in the formation of complete new segments ; 

 but one merome may be repeated so as to suggest several 

 metameres, whilst the remaining meromes are^ so to speak, 

 out of harmony with it and exhibit no repetition. Thus in 

 the hinder somites of the body of Apus the Crustacean we 

 find a series of segments corresponding apparently each to a 

 complete single somite, but when the appendages ai*e examined 

 we find that they have multiplied Avithout relation to the 

 other meromes of a somite ; Ave find that the somites carry 

 from two to seven pairs of appendages, increasing in number 

 as we pass backwards from the genital segment. The appen- 

 dages are autorhythmic meromes in this case. They take on 

 a quasi-independent metamerism, and are produced in numbers 

 Avhich have no relation to the numbers of the body-rings, 

 muscles, and neuromeres. This possibility of the inde- 

 pendent metameric multiplication of a single merome must 

 have great importance in the case of dislocated meromes, and 

 no doubt has application to some of the metameric phenomena 

 of Vertebrates. 



A case which appeal's at first sight to be one of " auto- 

 rhythmus'^ of the parapodia is that of the Diplopods (Julus, 

 etc.), in which each apparent somite carries two pairs of legs 

 or parapodia. It looks at first as though this were due to the 

 independent multiplication of the legs ; but it is not. Con- 

 trary to what obtains in Apus, we find in Julus that there is 

 a Avell-marked somite in the embryo corresponding to each 

 pair of legs, and that the adult condition arises from a fusion 

 of the tegumentary meromes of adjacent somites (see below, 

 "Fusion"). 



The Sixth Law is the law of dislocation of meromes. This 

 is a very important and striking phenomenon. A merome, 

 such as a pair of appendages (Aranea}) or a nouromere, or a 

 muscular mass (frequent), may (by either a gradual or sudden 

 process, we cannot always say which) quit the metamere to 

 which it belongs, and in which it originated, and pass by 

 actual physical transference to another metamere. Frequently 

 this new position is at a distance of several metameres from 



