1918] Morphology of Genitalia of Insects 113 



A marked deviation from the primitive condition is found in 

 the lack, apparent, at least, of appendages on the adult abdom- 

 inal somites. If one looks at the germ-band of an insect, how- 

 ever, one can see, soon after the appearance of the appendages 

 of the head and thorax, anlages of a pair of appendages for each 

 somite of the abdomen also. These rudiments are lateral, sac- 

 like swellings, usually pointing backward, and generally consid- 

 ered as serially homologous with the thoracic legs, as also with 

 the appendages of the head. 



The first account of embryonic limb rudiments on the first 

 abdominal somite of Gryllotalpa, was written by Rathke in 

 1844, and, later, on all the abdominal somites, by many others. 

 As we mean by primitive, in insects, that which shows their 

 close relationship to, and probable descent from, a myriapod- 

 like form consisting of several, successive, similar somites, each 

 having a pair of appendages, we are interested to look in the 

 adult for traces of the embryonic condition described above. 



4. Genitalia. — There is, at the caudal end of the abdomen 

 of every insect, a group of appendages having to do, more or 

 less directly, with the function of reproduction. Three pairs of 

 these appendages taken together are called, in a general way, 

 by German authors, " Geschlechtsanhange " ; by English and 

 American ones, "genital appendages," "genitalia," or "gona- 

 pophyses," the latter, a term introduced by Huxley in connection 

 with the Crustacea, and used by many others to indicate part 

 or all of these structures, in one or both sexes. They have also 

 been given, individually, names differing from one another in, 

 and characteristic of, each order, so that in some cases only a 

 systematist of the group concerned could follow a description 

 using them. These three pairs of appendages have been attrib- 

 uted to the three somites cephalad of the terminal or anal 

 somite, which, as explained in the foregoing, is considered the 

 eleventh by some and the tenth by others. 



It would seem natural to homologize these appendages with 

 the anlages of legs found respectively on the same somites of 

 the embryonic germ-band, but there are at least two opposed 

 views on this question. Lacaze-Duthiers, who published papers 

 on the subject in 1849-52, did not so consider them, but regarded 

 them as modified ventral sclerites of their respective urites, the 

 latter being the name by which this author, followed in this 

 respect by Berlese and others, called the abdominal somites. 



