656 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



matched it perfectly. The greater part of the body was bright green, but a few 

 white spots represented a broken ring of a lighter color; the edge was relieved by 

 dashes of black pigment, while the cirri were brownish. A very magnificent 

 example of the second type of coloration was found on a green form of Comanthus 

 annulatus. It resembled its host closely and was comparatively inconspicuous. 

 The general color was a bright green; the ridges appeared greenish white, darker 

 at the edges owing to the addition of a granular pigment, and around each there 

 was an intense black line. An allied form was found on darker crinoids. There 

 the ridges were white or yellow, surrounded by a darker line (in one case of 

 purple), and the ground color was brown. Lastly, in one or two forms almost 

 the whole upper surface may be covered by a dark pigment. Thus in one specimen 

 the dorsal surface was a dark green, only relieved by a white line down the middle, 

 while in another it was purple. These occurred on dark comatulids. 



Lieutenant Potts concludes that, on the whole, the myzostomes showed a great 

 color resemblance to their hosts, though striking exceptions occurred, and, even 

 when the color schemes harmonized, protection from human sight, at least, was 

 not always secured. 



The first published notice of a myzostome is found in Delle Chiaje's magnifi- 

 cent memoir on the invertebrate animals of the kingdom of Naples, which appeared 

 between 1822 and 1829. Delle Chiaje figured a myzostome on the disk of an 

 Antedon, but he interpreted it not as a parasitic organism, but as a madreporic 

 plate, comparable to the madreporic plates of the starfishes. 



Almost simultaneously F. S. Leuckart recognized these animals as peculiar 

 worms occurring on the comatulids, and in 1827 he described several species from 

 the Mediterranean and from the Bed Sea. 



John Vaughan Thompson, who in 1827 had discovered the pentacrinoid young 

 of Antedon bifida and subsequently had devoted much attention to this animal, 

 naturally had noticed the parasitic myzostomes, and in the paper in which he 

 announced the discovery that his Pentacrinus europa'us was nothing more nor 

 less than the young of Antedon bifida, published in 1835, he says of them : 



Connected with the natural history of the Cnmatula is that of a nondescript parasite which 

 appears to be a complete zoological puzzle, as it is not possible to determine from its figure 

 and structure to what class it ought to be referred. This little animal is figured * * 

 much magnified, its natural size not exceeding that of the breadth of the ossicula of the arms 

 of tie Cfimatula; it resembles a flat scale, runs about with considerable vivacity on the arms 

 of the animal, and occasionally protrudes a flexible tubular proboscis ending In a papillary 

 margin. The disk or body is surrounded by IS or 20 retractile and movable tentacula, and 

 beneath is furnished with five pair of short members, each ending In a hooked claw. Query, 

 is it a perfect animal or a larva, and does it belong to the Crustacea, Annelides, or what? 



In connection with his work upon the erinoids, Johannes Miiller in 1841 

 noticed Thompson's parasite and bestowed upon it the name of Cydocirra thomp- 

 sonii, at the same time expressing the opinion that Delle Chiaje's madreporic 

 plate was in reality a similar form. He entirely failed to see the connection 

 between these and the species which had been described by Leuckart in his new 

 genus Myzostomum. 



