72 Mr. W. S. Macrzav on the Structure of the Tarsus 
far as I have been able to observe, isa very accurate description 
of all those sand insects which are allied to Pimelia and Tenebrio. 
The manner, however, in which a Helops is heteromerous may 
perhaps be explained by examining the posterior pentamerous 
tarsus of Erotylus; in which case we should say that it is the 
penultimate joint of the tarsus that is evanescent in the Helo- 
pide. In the heteromerous Cistelene of M. Latreille we have a 
genus Mycterus, evidently allied to the Curculionide ; and a very 
careful dissection has made it appear to me that it is in reality 
pentamerous, only the third and fourth joints of the posterior tarsi 
are nearly confluent. Hence, in heteromerous insects generally, 
we may perhaps suppose that it is the fourth joint of the tarsus 
which vanishes. Isay generally, because there may be many ex- 
ceptions to the rule; perhaps, for instance, Meloe and the insects 
allied to it. These are true Heteromera ; but on looking at their 
posterior feet we find an obconical process, which seems to re- 
present the lost articulation, and occasions one almost to fancy, 
although not perhaps very philosophically, that it is the second 
joint of the tarsus which articulates with the tibia. The Linnean 
genus Cassida and Alurnus appear to have only four joints to their 
tarsus, which differs moreover from that of the Chrysomelide, in- 
asmuch as all these four articulations are dilated. The affinity of 
Cassida to Chrysomela shows us here also which joint is evanes- 
cent; and we find, in fact, that the last joint, although dilated at 
the extremity, puts on the appearance of the piece formed by the 
two last articulations of the tarsus in Chrysomela. This circum- 
stance may serve to throw light on the structure of the foot in 
Eumorphus, and the other insects commonly but erroneously 
called trimerous. I have shown them to be at least tetramerous ; 
and I conceive, from analogy, that it is the penultimate joint 
that is here also evanescent. But however this may be, enough 
has been said to prove the worthlessness of the tarsal system, 
even 
