NO. O INSECT ABDOMEN SNODGRASS 45 



bases of the second gonopods. In most pterygote insects each primi- 

 tive limb base of the ninth segment becomes differentiated into a 

 proximal second valvifer, and a free distal lobe, or third valvula. 

 In some of the lower insects the third valvulae bear small terminal 

 styli, which are usually lost in the adult stage. 



5. The third valvulae are secondary differentiations of the limb 

 bases of the second gonopods, forming free lobes at the distal ends of 

 the second valvifers. Usually they ensheath the distal part of the 

 ovipositor between their apposed inner surfaces, but in most of the 

 Orthoptera they resemble the gonapophyses, and form a third pair 

 of blades in the shaft of the ovipositor. 



6. The intervalvular sclerites are remnants of the ninth abdominal 

 sternum ; in some insects they give insertion to tergosternal and 

 other muscles. 



DEFINITIONS 



The following terms applied to the ovipositor and associated struc- 

 tures are here defined as used in this paper in order to make the 

 application clear, and to avoid the confusions of synonymy. 



Oviductiis laterales (Odl). — The paired oviducts, formed primarily 

 from the mesodermal strands continuous with the mesodermal sheaths 

 of the ovaries, but their posterior parts may be of ectodermal origin, 

 and in some cases the entire mesodermal ducts are said to be replaced 

 by ectoderm. The ducts are attached to the ectoderm at the posterior 

 border of the seventh segment in young stages of many insects, and 

 open at this position in adult Ephemerida, but in other adult insects 

 they are confluent in the anterior end of the median oviduct. 



Oviductus communis (Ode). — The median oviduct, of ectodermal 

 origin, opening in Dermaptera just behind the seventh abdominal 

 sternum, but in other insects extended to the eighth segment. 



Female gonopore (Gpr). — Any of the true oviducal apertures, 

 paired or median. The paired gonopores of Ephemerida and the 

 median gonopore of Dermaptera are on the posterior part of the 

 seventh abdominal segment ; the single female gonopore of other in- 

 sects is on or just behind the eighth sternum, where it is either ex- 

 posed externally or concealed in the genital chamber (copulatory 

 pouch, or vagina). 



Spermatheca, receptacidum seminis (Spt). — An ectodermal in- 

 vagination, usually single, but often double, and sometimes triple, 

 serving for the reception of the spermatozoa ; primarily formed on the 

 posterior part of the eighth abdominal segment, opening into the 

 anterior end of the genital chamber, or vagina, when this organ 

 is present. 



