560 John Beard 



larva finds its way to its host purely by chance. That is to say it is 

 merely carried to the Comatida by means of the currents of water caused 

 by the arms of the latter. If a larva, and especially such a minute one 

 as that of Myzostotna where caught by this current it w^ould in the na- 

 turai course of events be carried along the ambulacral groove towards 

 the mouth. If it were able by means of claws, or of some secretion, or 

 even by the use of its cilia, to save itself from being devoured, it would 

 stand a fair chance of further developraent, and would bave the means 

 of increasing rapidly its size in the food current passing along to the 

 mouth of its host. 



How it is able without claws to hold its own against the forces 

 tending to draw it into the mouth of the Comatula is not easily answered. 

 But that it does so in some way is certain. When possessed of two 

 pairs of claws, its position is pretty secure, for I bave observed that at 

 this stage they bave a very fimi hold on Comatula. In the tanks of the 

 aquarium of the Naples zoological station, the Comahdae sit in great 

 numbers on the stems of dead corals. But in addition a considerable 

 number take up their position near to or on the floor of the tank. Now 

 it has been shown that the larvae of Mijzostoma frequent the bottom, 

 and thus Comatulae on or near the bottom will be in a better position 

 for becoming host to larvae of Myzostoma than those further away. 

 Some observations made in the aquaria seem to show that this is really 

 the case, and thus that the current theory has some foundation. At one 

 time for some days on account of the stormy state of the sea, freshiy 

 caught Comaiulae were not to be had, and so I was obliged to fall back 

 upon those contained in the aquarium of the station, It was then noticed 

 that those Comatulae which were sitting on or near the bottom were 

 much more invested with Myzostoma than those which clung to the sides of 

 the tank or to the stems of the corals. It has been shown in the preceding 

 pages that the larvae are bottom forms, and a priori it is what one 

 might expect that individuai Comatulae which frequented the bottom 

 would be much more invested than those living at some distance from 

 it. In this connection it may be mentioned that a Comatula seldom or 

 never changes its position if not disturbed. I bave observed a Comatula 

 sit exactly in the sanie place on the stem of a dead coral for over a month 

 without changing its position. If this current theory be true an interesting 

 result would follow, viz. that only such larvae as were not too large to be 

 carried by this current would obtain a host and so be in a position for 

 further development. Thus the size of the larvae would be kept within 

 certain limits. Perhaps this is the reason, why the larvae are so small. 



