140 



MALE-STRUCTURES 



of testes, organs exhibiting much variety of form. The structure 

 may consist of an -ex'tremely long and fine convoluted tube, packed 

 into a small space and covered with a capsule ; or there may be 

 several shorter tubes. As another extreme may be mentioned the 

 existence of a number of small follicles opening into a common 

 tube, several of these small bodies forming together a testis. As 

 a rule each testis has its own capsiile, but cases occur — very 

 frequently in the Lepidoptera — in which the two testes are 

 enclosed in a common capsule ; so that there then appears to be 

 only one testis. The secretion of each testis is conveyed out- 

 wards by means of a slender tube, the vas deferens, and there are 

 always two such tubes, even when the two testes are placed 

 in one capsule. The vasa deferentia differ greatly in their 

 length in different Insects, and are in some cases many times the 

 length of the body ; they open into a common duct, the ductus 

 ejaculatorius. Usually at some part of the vas deferens there 

 exists a reservoir in the form of a sac or dilata- 

 tion, called the vesicula seminalis. There are 

 in the male, as well as in the female, frequently 

 diverticula, or glands, in connexion with the 

 sexual passages ; these sometimes exhibit very 

 remarkable forms, as in the common cockroach, 

 but their functions are quite obscure. There 

 is, as we have already remarked, extreme variety 

 in the details of the structure of the internal 

 reproductive apparatus in the male, and there are 

 a few cases in which the vasa deferentia do not 

 unite behind, but terminate in a pair of separate 

 orifices, 



the form of the sexual 



male as we have already mentioned it to be in 

 the corresponding parts of the female. 



Although the internal sexual organs are only 

 fully developed in the imago or terminal stage 

 of the individual life, yet in reality their rudi- 

 ments appear very early, and may be detected 

 from the embryo state onwards through the 

 other preparatory stages. 



The spermatozoa of a considerable number of 

 Insects, especially of Coleoptera, have been examined by Ballo- 



The genus Machilis is as remarkable in 

 glands and ducts of the 



Fig. 7 



cinctci. «, a, 

 testes ; 6, i, vasa 

 deferentia ; c, c, 

 vesiculee semin- 

 ales ; c?, extrem- 

 ity of body with 

 copulatory ar- 

 mature. (After 

 Dufour. ) 



