64 
THE VOYAGE OF H.M.S. CHALLENGER. 
the margin is covered with, short cirri, but the specimens were not sufficiently well 
preserved to enable me to fix the number ; on the two specimens mounted and preserved 
by v. Willemoes Suhm (one is displayed in fig. 11) only a few cirri (c.) were to be 
observed. In these specimens, however, the abundant ramification of the intestinal 
cseca was very distinct ; it is more abundant in this species than in any other. Cross 
sections show from twenty to thirty caeca on each side, irregularly branched. This rich 
ramification of the intestinal caeca, together with the form of the body and the existence 
of cirri, are the principal structural features that distinguish this species from the closely- 
allied Myzostoma deformator, with which it agrees in many other points, including the 
structure of the generative organs. It is, like the above-mentioned species, hermaphrodite, 
but differs from the typical free-living forms, in that the male generative opening and 
testis are only developed upon one side of the body ; the testicular follicles are concen- 
trated into a compact mass on one side, on the other there are only small rudiments of 
them, and the space generally occupied by these organs is filled with the highly-developed 
ovarian follicles. 
The individual shown in figs. 12 and 13 was 3 mm. long, the breadth of the animal 
rolled up was 1’7 mm. 
Host. — Pentacrinus alternicirrus, P. H. C., from , Station 214 (south-east of the 
Philippine Isles) of the Challenger Expedition. There were fourteen specimens of Penta- 
crinus dredged at this Station, some of which were inhabited by several, some by many, 
specimens of Myzostoma pentacrini, and had the arms enlarged. 
62. Myzostoma deformator, n. sp. (PI. XII. figs. 1-9). 
This species is parasitic in the pinnules, into which it bores its way in couples, causing 
them to become swollen and ovoid. This species is rarer than Myzostoma pentacrini. I 
examined four pinnules, three of which had the form shown in figs. 2 and 3, and no 
corresponding swelling of the arm-joint; in another one (figs. 4-6) the arm-joints ( a.-c .) 
were swollen too. 
The cysts have the same colour as the arm ; their walls are calcareous, of considerable 
thickness and hardness, and may be recognised as malformed pinnules by their mode of 
attachment to the arm, especially when (figs. 2,3) the ambulacral groove is continued along 
the whole length of the pinnule. The last-mentioned cyst measured 9 mm. in length, by 4*5 
mm. in breadth in the middle, and ended in an obtuse point about 1 mm. in length, into 
which the concavity of the cyst did not enter. The arm itself was not much altered, either 
in form or consistence, the only alteration was a slight swelling of the joint bearing the 
malformed pinnule (fig. 3), and a shortening of the pinnule of the other side (fig. 2 *) ; 
but it cannot be said with any certainty that this last-mentioned alteration has anything 
to do with the parasite in the opposite pinnule. As is always the case in this species, the 
