MEMBRA CIDJE. 
21 
Three tarsal joints are most commonly found in the Homoptera, but sometimes 
the first and second joints are so united that only two can be seen, even with a 
microscope. 
The division into monomerous, dimerous and trimerous groups seems nevertheless 
to follow very natural lines, and we accept the correctness of these divisions both 
morphologically and biologically, in the families of Homoptera, such as Cicadidee, 
Aphididse and Coccidee, &c. 
Unvarying rules cannot be framed to meet all cases in our classifications. The 
exceptions puzzle us. 
Insects with different numbers of tarsi on the fore and the hind legs are familiar 
amongst beetles and other insects. The division Heteromera amongst the Coleoptera 
is significant of incompleteness in our schemes. 
It is not difficult to state the normal number of digits in man and birds, but in 
microscopic insects the number of foot-joints often is not so obvious. 
The third tarsal joint is usually the longest, but the length varies with the genus, 
and there is much difference in length as we compare separate pairs of legs. As a 
generalisation, it ma}? - be taken that if there be a divergence in the number of tarsal 
joints of the Membracidse, the hind pair of legs in Membracis proper is trimerous, 
whilst the first and second pairs are dimerous or trimerous. The tarsi of the hind 
legs are often very weak and small. The trimerous tarsi are well seen in Umbonia 
and in Centrotus and its allies, in all their legs. 
The second tarsal joint is the smallest, and forms a hollow conical articulation, 
which is united to the first joint by its apex, and to the third by its base. An elastic 
membrane connects these joints, and gives free motion to the whole foot. 
The third joint ends with two hooked claws. In some species these claws are 
protected between two rounded pads, and then the foot seems to be terminated by 
pulvilli instead of claws. Where necessary, details of the legs of species will be 
found on the plates representing the entire insects. 
Before concluding this sketch of the external anatomy of the imaginal forms of 
Membracidse, we may call to remembrance the fact, that no system based alone on 
morphology can be regarded as perfect. 
Mr. W. F. Kirby remarks to the author that “ Nature is believed to have grown 
up into the form in which we now see it, from infinitesimal beginnings, by the 
effect of gradual changes acting and reacting on each other in the course of countless 
ages.” 
We are apt to ignore the fact that affinities often exist between groups and species, 
which in our necessary schemes we separate widely or ignore. 
The Immature Forms of Memhraciclce .—Where so little has been written about the 
