The Sexual Phases of Myzostoma. 
253 
individuals thus associated are very dissimilar in the entoparasitic 
species, it occurred to me that they miglit nevertheless be different 
developmental stages of the same species. This opinion was advanced 
in my preliminary paper ('94). I have since obtained sections which 
leave no doubt as to the correctness of my contention. This will 
appear from a consideration of the following stages. 
Stage 1. 0.5—0.8 mm long. Individuals in this stage have the 
appearance of PI. 12 Fig. 43. They are found on the dorsal or lateral 
surfaces — nsually the former — of the tongue-like caudal end or hid- 
ing under the reflected lateral and anterior edges of the large speci- 
mens. They are not so firmly attached as the young of M. glahrum but 
are capable of shifting their position quite rapidly, as Prouho has ob- 
served, on the densely ciliated integument of the subj acent Myzostome. 
In transverse sections (Fig. 46) passing through the middle of the body, 
there is no difficulty in distinguishing the intestine [hit] which is perfectly 
straight and without ramifications as yet, a small unbranched body- 
cavity [eoe] corresponding to the future »uterus«, well-developed para- 
podia provided with powerful hooks (s/), and a cylìndrical ganglionic 
mass [m] lying beneath the intestine. Embedded in the parenchyma 
on either side of the body is a large solid mass of testicular fol- 
licles [U] closely resembling those of the socalled male of the cysti- 
colous M. murrayi (cf. v. Graff 84 b, PI. 15 Fig. \ \t). In more ad- 
vanced individuals of this stage the small cells of these follicles 
are seen to be in active karyokinesis. Each testicle has a very 
short efferent duct opening on the surface. The penis, if present at 
ali, must be exceediügly small. Masses of very minute spermatozoa 
embedded in a plasmatic substance are often seen protruding from 
the male openings as indicated in the figure. The plasmatic sub- 
stance probably dissolves away in the water, as has been observed 
in other species, and sets the wriggling spermatozoa free. In this 
stage no traces of ovaries were to be found, and the individuals are 
really males, although it is probable that some of the peritoneal 
cells forming the walls of the uterus are already set apart as 
young oogonia. This point I have not as yet been able to deter- 
mine satisfactorily. 
Stage 2. 0.8—0.825 mm long. I have found only two spe- 
cimens of this stage among my limited amount of material, but they 
are of the utmost importance. 
The younger specimen (Fig. 47) measuring 0.825 mm in length 
has essentially the same outline in cross-section as the specimen 
