316 THE VOYAGE OF H.M.S. CHALLENGEK. 



vations appear to give additional support to the hypothesis which connects this group more 

 closely with the Tardigrada. Another interesting form is Myzostoma horologium (fig. 

 126a, b), which was taken in great numbers from specimens of Actinometra jukesi and 

 Actinometra strota, P. H. Carpenter, dredged at Stations 186 and 187 ; the disk has a 

 curious resemblance to the face of a watch, owing to the arrangement of the pigment on the 

 dorsal surface ; the parapodia and suckers are very stout and cirri are entirely absent. 



"Fig. 126c, represents another remarkable species, Myzostoma quadrifdum (host: 

 Antedon bidentata, P. H. C, Station 186), distinguished by the possession of four long- 

 caudal appendages ; there are many allied species which possess respectively two, four, or 

 six of these appendages. 



"Certain endoparasitic forms, obtained for the first time at Station 170, and subse- 

 quently at Stations 176 and 192, are of the highest interest, and differ greatly from all 

 other endoparasitic species by the peculiarities of their sexual organization, and by the 

 remarkable malformations which they produce upon the body of their hosts ; they may 

 be divided into two groups. The first group is hermaphrodite like the ectoparasitic 

 Myzostomida, but the male sexual apparatus, instead of being disposed symmetrically on 

 either side of the body, is only developed upon one side ; one to three individuals of 

 similar size and form are met with in the same cyst (fig. 127a, b, Myzostoma pentaenni 

 and Myzostoma deformator). In the second group the sexes are completely separated, 

 and the males and females differ from each other in external appearance, the former 

 being very small and delicate, while the latter are large and stout ; a single pair are found 

 associated together in each cyst (fig. 127c, d, e, Myzostoma tenuispinum, Myzostoma 

 willemoesii, and Myzostoma murrayi)} 



" The malformations produced by these species are of various kinds. In some cases 

 there are independent cyst-like swellings of the skin, as for instance the cyst of Myzostoma 

 murrayi (fig. 127e), which hangs down from the disk of Antedon radiospina, P. H. C. ; in 

 other cases the parasite causes more or less conspicuous swellings of the aims of the Crinoid 

 in the interior of which it lives; Myzostoma pentacrini (fig. 127a) and Myzostoma 

 tenuispinum (fig. 127c) form cysts of this description, the former upon the arms of 

 Pentacrinus alternicirrus, P. H. C, the latter upon Antedon angusticalyx, Antedon 

 basicurva, Antedon incisa, and Antedon inwqualis, P. H. C. Other species attach 

 themselves to the pinnules, which become variously swollen and contorted. Myzostoma 

 asymmetricum produces only a simple swelling and enlargement of the pinnules of 



1 The following is from the journal of the late Dr. R. v. Willemves-Suhm, under date 14th July 1874 : — " On the 

 pinnulfe of the Comatulse we found Myzostoma under rather peculiar conditions. Some of the pinnuhe had enlarged ex- 

 crescences and were rolled up so as to form a cavity, in which, in two cases, a larger and a smaller Myzostomum were found. 

 This reminds me very much of Trematodes, which, as in the case of Monostomum faba in the skin of birds, live always 

 in cases or sacs in pairs, one individual being much larger than the other, the one acting probably as male and the other 

 as female, which in some cases, as in Distoma okeni on the branchiae of Brama rayi, leads to a perfect diversity of sexes. 

 Perhaps something very similar takes place in Myzostomum, which is hermaphrodite, and has many affinities with the 

 Trematodes." 



