490 TEXT-BOOK OF ENTOMOLOGY 



the sexual glands are paired, not only in the larvae of all stages, but 

 also in the imagines, and in both sexes. In the males the vasa defer- 

 entia pass 011 the ventral side of the 9th segment through two 

 external appendages, both reproductive organs, at whose tips or sides 

 the openings are situated. In the larvae the female openings are 

 not formed until after the last moult. In the females the two ovi- 

 ducts open on the ventral side of the hind-body between the 7th and 

 8th segments. 



Palmen suggests that the Ephemerids represent, in respect to the 

 reproductive system among insects, a very primitive type of organi- 

 zation, and he concludes that the inner sexual organs of insects are 

 built up of two different morphological elements ; i.e. (a) internal 

 primitive paired structures (testes with vasa deferentia, ovaria with 



oviducts), and (6) integumental structures, 

 such as the ductus ejaculatorius and 

 vagina. 



In the younger larvee the vasa deferentia 

 form slender cords along which are situated 

 the seminal glands ; these cords are inserted 

 in the integument on the hinder edge of 

 the 9th sternite, where afterwards, during 

 the last moult, the copulatory organs grow 



FIG. 463. Upturned end of T , . -, , , -11 



body of Ephemera, with two egg- out. In the older larvae the sperm collects 



masses (o) issuing at the same time ,-, n ,v -i rm, 11 



from the double oviducts;?, anus, m the cavities of these cords. I heir walls 



become expanded, and this section then 



functions as vesiculse seminales. The ends of the cords remain con- 

 tracted and act as ductus ejaculatorii. Common unpaired glandular 

 structures are not present. At the last moult the copulatory organs 

 reach their complete development, and the ducts become open 

 externally. 



The oviducts in the larva are at first slender, string-like, and 

 bear the egg-follicles. As soon as the eggs pass out of the follicles 

 and collect in the oviducts, the walls of the latter become stretched, 

 and this portion forms two uterus-like structures. The terminal 

 division of the two passages forms their vaginal portions. But since 

 there is no common vagina, there are no unpaired glands and no 

 receptaculum seminis. The two ducts become open after the last 

 shedding of the skin. 



Palnien adds that this paired or double nature of the sexual glands 

 and their external ducts in this group of insects occurs in some Myrio- 

 poda (Fig. 3, E, F) and a few Arachnida (Fig. 3, C, D, the outlets 

 being in this class unpaired), numerous Crustacea, and most worms; 



