46 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Genital Ducts of Insects.* — J. A, Palmen has here a pre- 

 liminary note of his investigations into the comparative anatomy of 

 the efferent ducts of the sexual organs in insects. 



He commenced with the Ephemeridse which are, among insects, 

 remarkable for having the ducts paired, and that not only in all the 

 larval but also in the imaginal stages, and in both sexes. In the 

 males the two vasa deferentia extend, independently of one another, 

 as far as the ventral side of the ninth segment, where there are placed 

 the appended copulatory organs ; these the ducts traverse and open 

 at their tip or at the side. These appendages may be either almost 

 separate, or be more or less fused at their base ; in only one species 

 examined was there any transverse connection between the ducts. In 

 younger larvae the vasa deferentia are delicate cords along which are 

 placed the sperm-producing glands; in older larvae the sperm is 

 collected into the cavity of these cords, the walls of which become 

 enlarged, while the ducts have here the function of vesiculae seminales ; 

 the distal portion of the cord remains narrow and acts as an ejacula- 

 tory duct. 



In the female the two oviducts are also independent and open 

 between the seventh and eighth segments ; the fold in which the 

 orifices are placed has the chitinous layer of the body continued into 

 it, and this extends as far as the orifices of the oviducts. At first 

 delicate, the ducts become enlarged as the ova pass into them, and an 

 organ of uterine appearance is developed proximally, and a vagina 

 distally. On the whole it would seem to be clear that the Epheme- 

 ridae represent, so far as their sexual organs are concerned, a very 

 primitive type of organization. 



An examination of the structure and descriptions given of the 

 structure of the male organ in several species of Orthoptera and 

 Trichoptera seem to show that the unpaired ductus ejaculatorius of 

 these insects is morphologically an invagination of the integument 

 of the body. In the larvae of Corethra the two testes are attached to 

 the integument by two cords, and in Chironomus there is much the 

 same arrangement. During metamorphosis certain parts of the 

 hindermost abdominal segments are reduced and others increased 

 in size ; in consequence of this the points of insertion of the cords 

 — that is of the orifices of the vasa deferentia — pass inwards, 

 and this part of the integument becomes unpaired. In the Forficulinae 

 the azygous condition of the terminal portion of the male sexual ducts 

 is due to the development of an internal transverse connection between 

 the vasa deferentia, and the consequent reduction of one of the two 

 terminal portions. In this case, then, the unpaired ductus ejacula- 

 torius and the vesicles arise from the primitive vasa deferentia and 

 not from the integument. 



In the Perlidae, which stand close to the Ephemeridae, we find 

 that the oviducts open close to one another at the base of a median 

 unpaired vagina. Chitin invades this last, and here we have an un- 

 paired vagina which is, morphologically, a differentiated interseg- 



* Morphol. Jahrb., ix. (1883) pp. 169-76. 



