5. General Conclusions and Summaries. §Q 



degenerate male sex, the female being entirely suppresed. The curious and unexplained 

 protandry, which is almost invariable in all hermaphrodites, is suggestive in this connection, 

 and the bearing of this idea on the sexual relations in Cirripedia, especially with reference 

 to the complemental males, has been discussed in Chapter 2, pp. 33 — 37. 



There is a final topic for discussion, namely the connection between the theory of sex 

 here adopted and contemporary Mendelian theory. It is on many sides suggested that the 

 so-called determination of sex may take place in the germ before developement begins, and 

 we have already admitted, in consideration of the facts of transversely correlated hermaphro- 

 ditism etc., that this is probably the case, although the facts of parasitic castration on the 

 other hand force us to the conclusion that this "determination" is within certain limits of an 

 elastic character. It is interesting to observe that where an attempt has been successfully 

 made to find structural differences in the germ cells as possible indications of this early sexual 

 differentiation, the manner of this differentiation is in harmony with the results we have 

 obtained from the study of parasitic castration. The discoveries of Hexking, Mc Cluxg, Wilson 

 and others have shown that in many insects two kinds of spermatozoa exist differing in the 

 constitution of their chromosomes, while the eggs are apparently all the same. 



If we suppose that the two kinds of spermatozoa represent the male and female sex 

 respectively, while the eggs are purely female, we would obtain in the process of sexual 

 generation Va C? ? + 7a Q 2 , in which the male spermatozoa united with female eggs give 

 rise to males of really hermaphrodite constitution, while the female spermatozoa united with 

 female eggs give rise to females of pure female constitution. 



It is obvious that this interpretation is in strict agreement with the main conclusion 

 brought out in this chapter, viz. that males are potentially hermaphrodites, while females are 

 incapable of assuming the male characters. It is doubtful, however, whether this particular 

 "Mendelian" interpretation can be applied generally, because in some animals, e. g. the Bee, 

 it appears that the egg by itself is male and only becomes female through fertilization, while 

 in many Cladocera and Aphids females give rise parthenogenetically to males. 



It appears therefore that the primary mechanism of sex determination may be variously 

 distributed in the germ cells, but this need not affect the conclusions drawn from our side 

 of the question, namely from the reaction of a metabolic sexual substance to varying con- 

 ditions in the organism. The possible connection of this substance with particular chromo- 

 somes in the germ cells is at present outside the scope of experiment. 



The above discussion may be summarised in the following sentences: 



Summary of conclusions. 



1. The differentiation of the secondary sexual characters is not essentially dependent 

 on the presence of a differentiated gonad, but the differentiation of both primary and secon- 

 dary sexual characters is due to the evolution in the body of a third factor, which we may 

 call a sexual formative substance. 



Zool. Station zu Neapel, Fauna und Flora, Golf von Neapel. Rhizocepbala. 12 



