194 BULLETIN: MUSEUM OF COMPARATIVE ZOÓLOGY. 
PAGE PAGE 
11. Reproductive organs . +. 169 Testes and spermato- 
i Antony O , «bie 
Dion... e hie Genial guest l 
a. Peritoneal epithelium . 171 12. Phylogeny . . . s + + + 180 
b. Musculature . . . . 171 18. Bibliography = .. +. + + 183 
c. Connective tissue. . 172 Literature in which C. arenata is 
d. Internal epithelium CALR described or mentioned . . . 188 
Ovaries and oógenesis . 172 Explanation of Plates csg 
1. INTRODUCTION. 
Our knowledge of the Molpadiidae has hitherto been much less 
complete than that of the Synaptidae, Holothuriidae, and Cucuma- 
riidae, chiefly on account of the difficulty in obtaining an amount 
of material sufficient for a thorough study of any one form. It is 
true, that the researches of Semper (68), Kingsley (81), Danielssen 
and Koren (82), Ludwig (912), and others have in some measure 
acquainted us with the anatomical structure of this group, and that 
the investigations of Teuscher (76) and Jourdan (83) have thrown 
some light upon the histology of these forms; but it has seemed 
desirable to attempt with a sufficient amount of material at hand a 
somewhat more thorough investigation into both the anatomy and 
histology of the group. Hence I undertook, at the suggestion of 
my instructor, Dr. E. L. Mark, the study of Caudina arenata, 
specimens of which can sometimes be found in large numbers upon 
the sandy beaches near Boston, during or immediately after severe 
storms that are attended by easterly winds. 
During a residence of three years in Cambridge, I have visited 
Crescent Beach, Revere, Mass, whenever it seemed. to be at all 
probable that specimens of Caudina could be obtained. Often I have 
returned empty-handed, but at other times it has been possible in a 
single excursion to secure from one to fifty, or even more, indi- 
viduals. My endeavors to obtain embryological material have thus 
far been fruitless, Although in both sexes the sexual elements appear 
to be mature during the early spring, and male individuals in aquaria 
have at that time been observed in the act of emitting sperm (see 
p. 179), I have succeeded neither in obtaining ova that had been 
thrown out into the water, nor in finding either segmented or fer- 
tilized eggs within the female, nor in artificially fertilizing the eggs. 
