EEPOET ON THE MYZOSTOMIDA. 
11 
Sexual Organisation of the Myzostomicla Cysticola, 
Yon Willemoes Sulim 1 discovered, to his astonishment, that the individuals contained 
in a single cyst either resembled each other in form and size, or were very different, 
and concluded, though without having been able to examine the sexual organs, that in 
the latter case the individuals resembled Distoma olcenii, in that one had the male organs 
especially developed, and the other the female organs. 2 I am able to state that this is 
really the case, that each individual is either male or female, and that in addition the two 
sexes are unlike in appearance, the female being usually 50-100 times as large as the 
male. That these forms ( Myzostoma tenuispinum, Myzostoma willemdesii, Myzostoma 
inflator, Myzostoma murrayi) are originally descended from androgynous forms, in which 
the organs of one sex have become gradually abortive, is shown by the case of Myzos- 
toma cysticolum, in the female of which there are rudiments of the testes, but no male 
generative aperture (PI. XIII. fig. 4, t). These dioecious forms are also distinguished by 
the marginal position of the sexual apertures, both male and female (Pis. XIII. and XIV.), 
and the form of the testes in the males. In Myzostoma willemoesii and Myzostoma 
inflator alone, which resemble the free living forms in the possession of twenty long cirri, 
the testes have the typical ramified form ; in all the others they are compact roundish 
glands occupying definite areas in the lateral part of the body. 
In those forms in which the individuals inhabiting one cyst are not different in appear- 
ance, the sexual organs have a different structure ; each individual is here androgynous, 
but differs from the free living androgynous species in that the testis is developed only on 
one side of the body, and there is but one male genital aperture ; in Myzostoma pentacrini, 
however, there are small remnants of the other testis, but no second male aperture. 
The testis also, as in the dioecious forms, is a small compact gland. Since the testes of 
the dwarf males are fully developed on both sides, we must not regard the hermaphrodite 
species, Myzostoma pentacrini and Myzostoma deformator, as transitional between the 
typical hermaphrodite forms and those that are dioecious, but the latter must be derived 
independently from the free-living forms. 
More abundant materials are required before the question about the life history of 
the Myzostomicla Cysticola can be definitely answered, but my investigations permit me 
to state that the following view is in all probability correct. 
The male and female being found associated in a common cyst, and increasing in size 
with the growth of the cyst, shows that they perforate the arm -joints or pinnules of 
their host together. The growth of the cyst is of course caused by the presence of the 
parasite ; the female deposits her eggs within the cyst, and the young embryos, after they 
1 Yon Jer Challenger Expedition, Brief III., Zeitschr. f. wiss. Zool., Bd. xxv., 1875, p. xxxi., and Brief VI., Bd. 
xxvi., 1876, p. lxxix. 
2 “ Dass aucli liier (wie bei Distoma okenii ) das eine Thier sich namentlich fiir die mannliche, das andere fur die 
weibliche Thatigkeit entwickelt.” 
