228 
W. M.Wheeler 
Eisig for mach kind assistance and to Signor Lo Bianco for tbe 
abundance of Myzostome material with which he. supplied me. j 
woiild, moreover, express my sincerest thanksjo Prof. F. Jeffrey* 
Bell and to Dr. Günther of the South Kensington Museum for 
permission to examine the Challenger Crinoidea and v. Graff’s 
types of the Challenger Myzostomidae. The two gentlemen have 
also kindly allowed me to section and describe the new species of 
Mxjzostoma which I found while looking over the Crinoids. 
In the fixing of the different species of Myzostoma for histolo- 
gical study, I have obtained the best results with corrosive Subli- 
mate and the corrosive-acetic and picro-acetic mixtures. The sec- 
tions (5 — 7.5 y in thickness) were fixed to the slide by means of the j 
albumen and water method (see Bumpüs '94, pag. 721, and Toyama 
'94, pag. 126) and stained with Heidenhain’s iron-alum haematoxylin ' 
followed by a saturated aqueous solution of Orange G. The diffuse 
plasmatic stain of the Orange G forms an excellent background for | 
the black or blue of the haematoxylin. This method enabled me to , 
obtain a very clear — I might say, lithographic — stain. The variouS 
carmines and cochineals failed to give satisfactory pictures of the ' 
small nuclei and vague cell-contours which render the Myzostomidae 
so unfavorable from a histological standpoint. Even with the best 
results in staining, it is necessary to work almost constantly with an 
Immersion objective. 
Part I. Descriptive. 
V. Graff in bis taxonomic papers wisely refrained from sub- 
dividing the genus Myzostoma^ although he appears to have recog- 
nized the lack of uniformity in the species. He was doubtless well 
aware of the necessity of utilizing internal as well as external ana- 
tomical characters in delimiting groups of species, but the state of 
preservation of the Challenger specimens and their value as types 
made a thorough examination impossible. It is, perhaps, as well 
that the genus was not subdivided into several genera, for it now 
appears from facts to be recorded in the present paper, that the 
adolescent stages of several, and probably of all species of Myzostoma 
are remarkably similar in their Organization, although the adults 
may present differences to which a systematist might attach generic 
values. The final estimate of these characters must depend on a 
thorough morphological analysis of all the species of the group and 
