4 Papers from the Marine Biological Laboratory at Tortugas. 
located on Loggerhead Key, Florida. I take this occasion to acknowledge 
my indebtedness to the above Institution, and particularly to Dr. Alfred G. 
Mayer, director of the Laboratory, whose cordiality, unstinted aid, and kind- 
ness have made this much of the work possible and the collection of the 
material a real pleasure. Of Ophiocoma there was very abundant material 
on the reef near Dry Tortugas. These eggs were almost ripe at the time 
of my departure from the key. The sperm were already ripe and very 
active at this time. Of Echinaster only a single specimen was found, and 
this quite accidentally in the moat about Fort Jefferson. I have since 
learned that this form is very abundant at the Marquesas Keys and I hope 
to obtain material from there during the coming summer. This appears to 
be a most promising object for future study. 
The ovarian material was fixed in the sublimate acetic mixture. The 
sections were cut at 8 micra and stained according to Heidenhain’s iron- 
hematoxylin method and some were counterstained with eosin. The accom- 
panying drawings were made with a Bausch and Lomb 4g oil-immersion 
lens with a No. 1 ocular, the outlines being obtained by aid of an Abbe 
camera lucida with the drawing surface 150 mm. below the level of the 
stage. The details were filled in free hand after study with a Zeiss 2 mm., 
aperture 1.30 apochromatic lens. 
ECHINASTER CRASSISPINA. 
The egg of this species at the culmination of the growth-period is very 
large (fig. 5, a). Its nucleus has a diameter of about 300 micra. The cyto- 
plasm is of a beautiful large alveolar type (fig. 7). In the preserved 
material the nucleoplasm has contracted, leaving a lacuna which is partially 
filled with a homogeneous coagulum. The nucleoplasm is also homo- 
geneous or very finely granular and non-stainable in basic dyes. Scattered 
throughout the nucleus are very many (a hundred or more) chromatic 
masses, most of which have the form of typical tetrads (fig. 5, 0). Study 
of abundant transition stages from the ovum at the beginning of the growth- 
period to the full-grown egg above described reveals the complete and con- 
tinuous history of the origin and development of the characteristic features 
of the nucleus and cytoplasm. 
The very young egg (figure 1) is already large as compared with the 
eggs of most echinoderms. It is surrounded by a very thin nucleated 
membrane of the ovarian stroma. Its cytoplasm is coarsely granular. The 
nucleus frequently appears shrunken away from one side of its wall, leaving 
a crescentic lacuna. The nuclear reticulum is delicate, coarse-meshed, and 
pale-staining, with occasional flakes of chromatic material. The nucleolus 
is intensely chromatic, homogeneous, and of sharp outline. A slightly later 
stage shows very decided alterations, both in the cytoplasm and nucleoplasm 
(fig. 2). Many of the cytoplasmic granules have become greatly enlarged 
