A STUDY OF METAMERISM. 437 



ou in the cells of the autennse before each moult will deter- 

 mine where the new lines of division between the segments 

 come in, and in some way the bent condition of the antenna 

 seems to effect to a large extent the formation of the new 

 lines. 



I have also examined the development of the antennae in the 

 lobster. At the third (?) moult the terminal division of the 

 endopodite of the antenna contains within it a rod of cells, and 

 these show alternate constrictions to form the lines between 

 consecutive rings. These lines of constriction are exceedingly 

 near to one another, since the segment containing the new series 

 is considerably shorter than the total number of segments that 

 ultimately develop from it at the next moult. It is easy to 

 see that under these cramped conditions the arrangement of 

 the division lines might easily be disturbed by local causes. 



An examination of the antennae of certain insects where 

 regeneration of the antennse of the adult is not probable (and 

 that in the larva hardly possible) shows that in those forms 

 where there are a large number of rings, and each ring very 

 short, variations exist in the arrangement, while in those 

 forms with long rings such variations are absent (or not found 

 commonly). 



In the locust I have not seen any misformed rings in the 

 antennae (in as many as fifty individuals examined). In the 

 cockroach (Blatta), where the rings are narrow, compound seg- 

 ments and short spirals are frequently found both in the larvae 

 and the adults. 



X. Abnormal Metamerism of Locust. 



It seemed to me highly improbable that such specialised 

 raetameric forms as the Crustacea and Insecta, in which the 

 metameres are so definitely limited in function, number, and 

 position, should show any variations comparable to those in 

 the earthworm. However, I had brought to me a locust 

 (''grasshopper^^) in which there was a half-segment more on 

 one side of the abdomen than on the other. 



In fig. 89, A, is drawn a dorsal view of this locust with the 



