THE MALE REPRODUCTIVE ORGANS 



485 



Insects are without exception unisexual, the male and female 

 organs existing in different individuals, no insects being normally 

 hermaphroditic. The reproductive organs are situated in the hind- 

 body or abdomen, especially near the end, the genital glands opening 

 externally either in the space between the Tth and 8th, or 8th and 

 9th, or 9th and 10th abdominal segments, but as a rule between the 

 8th and 9th segments (Fig. 299). 



The primary or essential male organs are the testes, those of the 

 female being the ovaries. As we shall see, the primitive number of 

 seminal ducts and oviducts was two, this number being still retained 

 in Lepisma and the Ephemeridae. The reproductive organs of both 

 sexes are at first, in their embryonic condition, of the same shape 

 and structure, becoming differentiated in form and function before 

 sexual maturity. These glands and ducts have a paired mesodermal 

 genital rudiment, the ends of the ducts being often connected with 

 corresponding ectodermal invaginations of the cuticle. 



The secondary sexual organs mainly comprise the external geni- 

 tal armature of the male, and the egg-laying organs, or ovipositor of 

 the female. Besides these structures there are other more superfi- 

 cial secondary sexual characters, such as differences in the size and 

 ornamentation as well as coloring" of the body, or of parts of it. 



The primary sexual organs of insects have been conveniently tab- 

 ulated by Kolbe, thus : 



I. Male reproductive organs. 



1. Two testes, with testicular fol- 



licles. 



2. Seminal ducts (vasa deferen- 



tia). 



3. Seminal vesicle. 



4. Accessory glands. 



5. The common seminal outlet, 



with the penis. 



6. The copulatory apparatus. 



II. Female reproductive organs. 



1. Two ovaries, with the egg- 



tubes. 



2. Two oviducts. 



3. Receptaculum seminis ; bursa 



copulatrix. 



4. Accessory sac. 



5. The common oviduct, vagina, 



uterus. 



6. The ovipositor. 



The ducts of the sexual glands in Peripatus being transformed nephridia or 

 segtnental organs, it has been inferred that this is also the case with those of 

 insects, though, as Lang states, there is a considerable difference in the two 

 cases, as the greater part of the ducts in Peripatus arises out of the ectoderm, 

 while in the Myriopoda and insects they come from the mesoderm ; but he adds 

 that in the Annelids the greater part of the nephridial duct is of mesodermal 

 origin. 



