72 Mi'sceUdneous. 



dorsal Rurfap<> of ^fl/z<).ttollla ahtlum what arc supjiosed to be com- 

 plomontal malos to tho miinbcr of ono or two, whii-li exactly reoall 

 tho<f which wore descrilied by Beard in Mi/:ostoma rflahrum, and 

 which von Graft" had probably been right in considering as young 

 ones. Now a scries of observations has convinced me, without any 

 possible doubt, that the individuals attaclied to the dorsum of the 

 hermaphrodite J///ros/o»ta ff/(«^nn are young ones of the same species, 

 which, while they are males in their youth, with well-developed 

 spermatozoa and vasa deferentia equal to those of the adult, incrca/ie 

 in size and acquire durinrf cjrowth ovaries ivliich are i<lentical with 

 tho^e of the hermaphrodite form ivhirh hears them, and this without 

 abandonini; the dorsal surface of the latter. These supposed comple- 

 mental males moreover possess, even in their youth and at a time 

 when they show no trace of ovaries, genital duets corresponding to 

 the female genital ducts of the hermaphrodites (a fact which hiis 

 already been observed by Xansen in Mifzostoma yigantcum and 

 M. Carpenteri). 



The complemental male therefore has no existence, in the proper 

 sense of the word, in the case of Miizostoma alattim. This species is 

 a proteraudrous hermaphrodite form, in which the two male and 

 female genital glands coexist in the adult. That the young male at 

 the outset of its existence plays the part of a complemental is 

 possible, but it is not proved ; and in all cases its male condition is 

 only transitory, which indicates perhaps that hermaphroditism in 

 Jlifzostoma is an acquired condition, and not a primitive one. 



I do not as yet possess proof that the complemental males of 

 Miizostoma r/lahrum also acqtiire ovaries ; but the facts which I have 

 observed in the case of Miizostoma alatum lead me to believe that 

 they do. 



In conclusion, I would remark that the four species of Miizostoma 

 with which we are at present acquainted as existing in the Mediter- 

 ranean ])resent us with three, or perhaps even with four, types, 

 which are of interest from the point of view of the sexual organi- 

 zation of the genus Myzostonia, viz. : — 



Hermaphrodite type, Mijzostoma r'lrriferxm. 

 Proterandrous hermaphrodite type, Mjizostinii alatnm. 

 Hermaphrodite typo with conjplemental male(?), Myzostoma 



ainhrum. 

 Dioecious ty2)c witli dwarf mab', Myzustoma pulvinar. 



— Comptesliendns, t. cxv. no. 20 (November 14, 1S92), pp. 8-16-S49. 



