The Sexual Conditions of Myzostoma glabrum (F. S. Leuckart). 319 



Paragraph 7 (pag. 267). As to Nansen's organs, ìt may be con- 

 ceded, that no reasons would appear to exist for terming tbem rudi- 

 mentary. They are probabl}^ the originai sexual organs, wbieb 

 existed prior to the adoption of the parasitic mode of life. They 

 stili function, but not as the sole sexual organs. In the herma- 

 phrodites they represent ovaries, in the males testes. With the 

 adoption of the parasitic mode of life, greater demands were made 

 on the reproductive powers, and the sexual organs were reinforced 

 by the conversion ^ of other parts, almost the wbole, of the peritoneum 

 to reproductive purposes for the production of eggs and spermatozoa -. 

 No-one denies that sperm-cells arise bere and tbere from cells of 

 the peritoneum (comp. fig. 13), and ali investigators of Myzostoma^ 

 with the sole exception of Wheeler, agree, that eggs also bave a 

 like origin (comp. figs. 2, C, 10, etc.). 



This is abundantly demonstrated in the i)resent writing, and 

 Prouho (7) has, in Opposition to Wheeler's conclusions, stated results 

 identical with mine. 



Paragraph 8 (pag. 268). With reference to the statement, quoted 

 from my paper by Wheelek, to the efifect, that »many of the extreme 

 cysticolous forms bave been shown to be dioecious«, while I hold 

 this to be correct — for notbing has been proved regarding tbeir 

 sexual characters beyond that they are dioecious — it may be 

 granted, tbat some of tbem may turn out to be more or less herma- 

 phrodite. But, at the same time, the right must be denied to 

 Wheeler, to make the assumption in the present state of our 

 knowledge, that tbey, or any of those hitherto regarded as dicecious, 

 are protandric bermaphrodites^. Argument from analogy, which 



1 Or better, perhaps, by the extension of sexual cells into these. 



2 It must be noted that bere, as shown by Pelseneer to bave been the 

 case in certain Mollusca, the females bave been converted into hermapbrodites, 

 and thus the persistence of the originai ovary as an ovary is explicable. 



3 In a foot-note on pag. 259 Wheeler indicates how in accordance with 

 the conditions created by his conception of the domestic economy of the 

 Myzostomidte in general the association of a larger and snialler individuai — 

 respectively »senior« and »junior« according to him — in a cyst comes about. 

 He writes: — »I believe tliat, in the case of the cysticolous species, the gali 

 must be formed by a single individuai, and that later a young Myzostome, wheu 

 it abandons its pelagic trochophore stage, must enter through the aperture of 

 the gali, and settle down to a quiet life with the senior individuai. The latter 

 probably dies at the end of its female stage and, undergoing decomposition, 

 may perhaps serve as food [!] for its stili vigorous junior partner. This one in 

 turn may there upon become the senior partner of another young Myzostome, 



