The Sexual Phases of Myzostoma. 
257 
sides a numher of deeply staining irregulär graniiles, a pale round 
body, whicli I hesitate to Interpret as a nucleus although it is certainly 
remarkable tliat no other structure comparable to a nucleus could 
be found in tbese amoeboid organisms wben they had been treated 
with such an excellent nuclear stain as Heidenhain's iron-haema- 
toxylin. 
Distoma myzostomatis n. sp. 
From 1 to 5 of tbese parasites were found in eacb of the sectioned 
specimens of M. plaiypus. They usually occurred in the parenchyma 
of the wall of the pharynx near its anterior end and were ali 
without exception young specimens. Two of tbese parasites wliicb 
happened to be sectioned in a favorable piane are shown in PI. 12 
Fig. 51. The upper parasite in the figure is cut sagittally, the lower 
horizontally. The two suckers (ac.o and ac.v) and the pharynx [ph] 
lying between them are distinctly seen. The region between the two 
suckers is encircled with a girdle of dark pigment [pg] which was 
Constant in ali the specimens. It invades the deeper tissues of the 
body as shown in the upper parasite. It was also possible to detect 
rudiments of the reproductive organs gd) and of the excretory 
system [neph). In some cases a small piece of the pharyngeal 
parenchyma of the host had been drawn into the median sucker of 
the Distome, as shown in the upper parasite of Fig. 51 [q). 
These data are, of course, too brief to be of any Service in 
determining the life history of this Distome, which must be an 
interesting one, living as it does in the tissues of a host which in 
turn lives in the tissues of a second host, a singular case of em- 
boìtement, or scatulation — a Trematode within a Myzostome, a 
Myzostome within a Crinoid. 
Part II. General Considerations. 
a. Historical and Criticai. 
In the minds of the older authors, Lovén ('42), Schultze ('54), 
0. Schmidt ('57), and Semper ('57) there was no doubt concerning 
the sex of the Myzostomidae. The common European species, in those 
days the only species known, were at once set down as hermaphro- 
dites — an inferencé which was, of course, perfectly justified by the 
Observation that both ova and spermatozoa were formed in the same 
individuai. 
