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 %2 oil-immersion 

 lens with a No. i 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 i .30 apochromatic lens. 



ECHINASTER CRASS1SP1NA. 



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, &). 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 i) 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 



