GENITAL ORGANS. 351 



part of the originally hermaphrodite genital rudiment, and may, in 

 individual cases, even develop imperfect ovarian tubes and eggs. 

 It has yet to be proved that the vestigial organs found in the adult 

 male have originated from this remnant of the genital rudiment. 



HEYMONS concludes from the above observations that hermaphroditism was 

 the original condition in the ancestors of the Insecta. This view, if correct, 

 would account for the frequent occurrence of hermaphroditic conditions in adult 

 Insects. 



In the female, the whole rudiment of the primitive efferent ducts 

 is directly transformed into the oviduct. In the male, on the 

 contrary, the whole length of this rudiment does not become trans- 

 formed into the vas deferens, but its distal terminal portion 

 degenerates and is replaced by a secondary terminal section, which 

 then becomes connected with the ectodermal ductus ejaculatorius. 



If we pass in review the origin of the genital organs, as shown 

 in the above description* of Phyllodromia, we have first of all to 

 point out that, in the derivation of the genital cells from the epithelium 

 of the coelomic sacs, we find direct agreement with the Annelida.! 

 In the later development of the paired genital gland and of an 

 efferent duct directly connected with it, there is a certain resemblance 

 to the condition found in the Onychophora (p. 208). The dorsal 

 position of the glands in these two Arthropodan groups is a special 

 point of agreement. On the other hand, it should be pointed out 

 that the genital gland of Peripatus, according to Sedgwick, arises 

 by the direct fusion of the consecutive coelomic sacs (the Myriopoda 

 have been placed in the same category by Heathcote, p. 252), and 

 that therefore, in Peripatus, the genital cavity comes from the 

 coelomic sacs. In the Insecta, on the contrary, the genital rudiment 

 lies, indeed, in the wall of the coelomic sacs, but the lumen of 

 the efferent duct here arises independently of the coelomic sacs, the 

 cavities of the latter forming a small part of the permanent body- 

 cavity. From this point of view, we shall have to regard the 



* The fact that this description not only applies to Phyllodromia, but is 

 approximately applicable to many other Insects, perhaps to all, seems to be 

 shown by the harmonious though fragmentary statements of Heidek and 

 WHEELER with regard to the Coleoptera. 



t [It would seem highly probable, from recent researches on the origin of the 

 germ-cells in various Invertebrata, that these cells, although not always to be 

 distinguished by our limited vision from the general mesoderm, and especially 

 from the coelomic epithelium, are in reality quite distinct from an early 

 cleavage-period, and differ essentially from the mesoderm-cells in their nuclear 

 organisation. This is rendered probable from the researches of HEETWIG on 

 Sagitta, Haeckeh on Cyclops, Boveri and others on Ascaris, Weismann on 

 Chironomus. — Ed.] 



