72 Miscellaneous. 



dorsal surface of Miiznstoma alatum what are supposed to be com- 

 plemeutal males to the number of one or two, which exactly recall 

 those which were described bj^ Beaixl in Myzostomci glabncm, and 

 which von Graff had probably been right in considering as young 

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

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

 hermaphrodite Mifzostoma aldtum 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, increase 

 in size and acquire durinrj cfrowth ovaricii tvMch are identical luith 

 those of the hermaphrodite form, whirh bears them, and this without 

 abandoning 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 ducts corresponding to 

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

 already been observed by Hansen in Mijzostomci gigantaun and 

 M. Carpenteri). 



The complement al male therefore has no existence, in the proper 

 sense of the word, in the case of Myzostoma alatum. This species is 

 a proterandrous 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 

 j\lyzostonta is an acquired condition, and not a primitive one. 



I do not as j-et possess proof that the complemental males of 

 Myzostoma gJahnim also accjuire ovaries ; but the facts which I have 

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

 they do. 



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

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

 ranean present 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 Myzostoma, viz. : — 



Herma])hrodite type, Myzostoma. cirri fernm. 

 Proterandrous hermaphrodite type, Myzostoma alatum. 

 Heima})hrodite type with complemental male(?), Myzostoma 



glahrum. 

 Dioecious type with dwarf male, Myzostoma paJvinar. 



— Compti-s Kendas, t. cxv, no. 20 (jS^ovember 14, 1892), pp. 8-16 ^8-19. 



