402 



HIRUDINEA 



testis. Later both testis and duct become hollowed out with 

 common cavity. The main portion of the vas deferens of each 

 side, as well as the terminal copulatory apparatus, is an ingrowth 

 from the epidermis which meets the downgrowths from the testes. 

 That there are considerable differences between the repro- 

 ductive organs of the leeches and those of Oligochaeta will be 

 apparent from the above description. There are, however, to 

 begin with, certain obvious similarities. In the first place, 

 the origin of the reproductive glands is identical ; in both groups 

 also the efferent ducts consist of two portions an invagination 

 from the outside, and a formation of the proximal part of the 

 ducts near to the glands. In Moniligaster, where exceptionally 

 the testes develop on the posterior wall of their segment in 

 close contact with the funnels of the sperm- ducts, there is no very 

 hard and fast line to be observed between the 

 tissues of the two. The hollowing out of the 

 testis in the leech, and the continuity of the 

 cavity thus formed with the duct, is a specialty 

 of the leeches not found among the Oligochaeta. 

 Like many Oligochaeta, the leeches may form 

 spermatophores in which the sperm is packed for 

 its conveyance from one individual to another. 

 Glossiphonia {Clef sine) plana, where the structure 

 in question has been elaborately described by 

 Whitman, 1 may be selected as an example. The 

 spermatophore (Fig. 209) is about 8 mm. long, 

 and is clearly formed of two halves, each of which 

 is formed separately in one ductus ejaculatorius, 

 the soldering together being effected in the 

 common part of the male ducts, where also a 

 basal portion with a single lumen is added. 

 The spermatophore has a double wall. It is 

 deposited not in the neighbourhood of the 

 ^tophoreof^S- generative pores, but upon the back ; and Whit- 

 phonia plana. man nas discovered the extraordinary fact that 



!il 



x 22 (After 



Whitman.) the spermatozoa find their way through the body- 



wall of the leech into the interior of its body, 

 where fertilisation presumably occurs. 



1 " Spermatopliores as a Means of Hypodermic Impregnation," J. Morphol. ii 

 1891, p. 361. 



