RESULTS OF CROSSING TWO HEMIPTEROUS SPECIES. 481 



the development of the male reproductive glands would also carry the 

 factors necessary for the development of the intromittent organ w^hich, when 

 present, is functionally a necessary adjunct of the glands, and as indicative 

 of the sex as the reproductive glands themselves. If we cannot accept the 

 mode of transmission of the intromittent organ as an index of the mode of 

 transmission of the reproductive glands, it would seem necessary to discard 

 all structural features or other characters which are distinctive of the gonads 

 of a given species, such as their distinction in size, form, colour, etc., and 

 assume that these characters, associated with the gland, have a different 

 mode of transmission from the gland itself. 



This would prevent any experimental test being applied to the chromosome- 

 theories of sex-determination and leave free scope for the wildest cytological 

 speculations. If we should place the intromittent organ in the group of 

 secondary sexual characters, because it has certain features in common with 

 these characters, we ought logically to place the reproductive glands them- 

 selves in the same group. For example, both these organs, in common with 

 most of the secondary sexual characters, can be transmitted to the opposite 

 sex — hermaphrodites appearing in forms that are normally sexually distinct 

 A case in point is Goodrich's ('12) interesting and important discovery of a 

 male amphioxus in which 49 of the gonads were testes containing ripe 

 spermatozoa and one was an ovary containing ripe ova. It may be urged 

 that the intromittent organ is a secondary sexual character on the evidence 

 that in the development of the embryo it appears much later than do the 

 gonads — this indicating that the gonads are more fundamental and stable 

 morphological entities. But there are facts opposed to this interpretation — 

 Smith ('10) found that when the spider crab is infected by the parasite 

 sacculina, the testes can become so greatly metamorphosed that some of the 

 cells may develop into ova and the same testis contain both ripe ova and 

 spermatozoa. 



It would seem that the division between primary and secondary sexual 

 characters, in common with almost all attempts at classification, has the 

 objection that the line of demarcation is not, at all points, perfectly clear ; 

 but we believe, in spite of this, that we are justified in classing the intro- 

 mittent organ as a primary sexual character, and that the results from the 

 study of the transmission of this organ may justly be claimed as an index of 

 the method of transmission of the reproductive glands themselves.- 



In the case of the genital spot the bearing of our results on recent 

 chromosome-theorios has been fully discussed in our earlier papers. We believe 

 we clearly demonstrated that the facts are entirely out of harmony with all 

 those hypotheses which claim to offer an explanation of the transmission of 

 characters by the assumption that factors essential to their transmission are 

 carried and distributed by definite chromosomes. 



