654 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



3. An androgynous or functionally hermaphroditic phase, extending from the 

 appearance of the first ripe ova to the disappearance of the last ripe sperma- 

 tozoa (hermaphroditic stage). 



4. A hysterogynous phase extending from the disappearance of the last sper- 

 matozoa to the disappearance of the last ripe ova, an event which is very probably 

 not attained at the time of the animal's death (female). 



Wheeler states that in M. pulvinar, and probably in many of the cysticolous 

 species which are supposed to be dioscious, the male phase ( $ ) is very short and 

 terminates before the retarded appearance of the first mature ova, so that this 

 species lacks a functionally hermaphroditic stage ( 3 ) corresponding to that of 

 M. cirriferum and M. parasiticum, and instead there intervenes a period during 

 which the animal grows but does not produce spermatozoa or ova ; hence when a 

 number of specimens are examined this sharp separation of the male and female 

 phases in time has superficially the same appearance as the separation in space 

 in gonochoristic forms with dwarf males. 



Among the other animals parasitic on crinoids an exactly similar asynchronism 

 and sequence in the ripening of the sexual products occurs in Anilocra. 



To determine the relative abundance of Myzostomum glabrum and M. cir- 

 riferum von Graff examined 323 Antedons from Trieste (adriatica), Pirano 

 (adriatica} , Naples (mediterranea) , and Messina (mediterranea) , and found 123 

 specimens of M. glabrum and over 1,600 of M. cirriferum. 



The relative abundance of the two species is thus 1 :14, and on the average 

 there are 5.3 Myzostoma on each Antedon, 4.9 cirriferum, and 0.38 M. glabrum; 

 or, each Antedon from the Mediterranean bears on the average 4 to 5 M. cirriferum, 

 and each third Antedon 1 M. glabrum. But these averages do not represent the 

 true state of affairs, for fully a third of the Antedons are entirely free from these 

 parasites. Of the 323 examined, not quite two-thirds carried M. cirriferum, while 

 scarcely one-fourth carried M. glabrum; and while M. cirriferum almost always 

 was present in greater numbers than M. glabrum, occasionally M. glabrum 

 occurred in greater numbers than M. cirriferum. 



The 123 specimens of M. glabrum were taken from 69 Antedons, on which 

 they occurred with the following frequency : 



On 39 Antedons, 1. On 3 Antedons, L 



On 15 Antedons, 2. On 1 Antedon, 5. 



On 10 Antedons, 3. On 1 Antedon, 7. 



While as a rule there are rarely more than 3 M. glabrum on a single Antedon, 

 there are commonly from 6 to 8 or more M. cirriferum, and on a specimen of 

 A. adriatica from Trieste von Graff found no less than 27 of the latter. 



On a specimen of Tropiometra macrodixcus collected by Mr. Alan Owston in 

 southern Japan I found 93 rather large myzostomes. 



The dorsal surface is sculptured only in the larger species, which are also 

 often distinguished by large elevations and ridges on the surface of the body. 

 This sculpturing, when present, takes various forms; the dorsal surface may be 

 covered by fine folds; the skin may be divided by longitudinal and cross furrows 



