NO. 8 INSECT ABDOMEN — SNODGRASS 47 



Suhgcnital plate. — The exposed sternal plate beneath the genital 

 apparatus ; primarily the eighth abdominal sternum, but the seventh 

 when the latter underlies and conceals the reduced eighth sternum, 

 or the ninth sternum when the vaginal opening is transferred to the 

 ninth segment. 



Vagina (Vag). — The genital chamber when the latter takes on a 

 pouchlike or tubular form with a narrowed posterior opening ; in some 

 insects extended into the ninth segment to open on or behind the 

 ninth sternum. 



Ostium vaginae, or vulva (Vul). — The external opening of the 

 copulatory pouch or vagina, on either the eighth or the ninth ab- 

 dominal segment, serving usually both for copulation and for the 

 discharge of the eggs. 



Bursa copulatrix. — Any cavity of the female serving for the recep- 

 tion of the male organ of copulation ; usually the genital chamber or 

 its derivative, the vagina ; in most Lepidoptera a diverticulum of the 

 genital chamber invagination on the eighth abdominal segment. 



V. THE OVIPOSITOR OF ORTHOPTERA 



The ovipositor of orthopteroid insects presents three types of struc- 

 ture. It occurs in a reduced and in some cases a more or less modified 

 form in Phasmidae, Mantidae, and Blattidae ; it is normally developed 

 in Grylloblattidae, Tettigoniidae, and Gryllidae, and attains its great- 

 est mechanical perfection in the last family ; finally, it is most special- 

 ized and modified in structure in Acrididae and Tridactylidae. For a 

 general account of the ovipositor in these several families the student 

 is referred to the paper by Walker (1919) on the terminal structures 

 of orthopteroid insects ; the comparative musculature of the ovipositor 

 is described by Ford (1923). The morphology and mechanism of the 

 organ will be illustrated here from studies made on Blatta and Gryllus, 

 forms representing the first and second types of structure noted 

 above ; a description of the specialized acridid type will be reserved 

 for a future paper. 



The ovipositor of Grylloblattidae, Tettigoniidae, Gryllidae, and 

 Acrididae differs from the ovipositor of other insects in that the third 

 valvulae enter into the formation of the shaft of the organ, which 

 thus consists of three pairs of appendicular blades or lobes, which are 

 the first, second, and third valvulae as here named. Because of their 

 usual positions relative to one another in the Orthoptera, the three 

 pairs of blades are distinguished by Walker (1919) as dorsal, ventral, 

 and inner valvulae, or correspondingly by Chopard (1920) as valves 



