DEPARTMENT OF MARINE BIOtOGY. 139 



The Annelid Fauna of Tortugas, by Aaron L. Treadwell, of Vassar College. 



My objects in going to the Tortugas Laboratory were (i) to collect as ex- 

 tensive a series as possible of the Polychseta of the region, and (2) to con- 

 tinue observations begun elsewhere on the embryology of this group. 



While extensive collections of Polychseta have been made in the West In- 

 dian region, these have been mostly of the deeper-water forms, very little 

 being known of the annelids of the shallower waters. There are no mud-flats 

 at the Tortugas, the nearest approach to one being the bottom of the moat at 

 Fort Jefferson. There a few burrowing forms occur, but elsewhere annelids 

 are found only in crevices of the coral rock, where a very large number are 

 to be found in the dead rock, and even, as in the case of some of the Sabel- 

 lidge growing through the living coral, the brilliantly colored gills of the 

 annelid protruding from the surface of the rock by the side of the coral 

 polyps. Approximately 50 genera were collected, the largest number of 

 genera being representatives of the Eunicidse. 



Observations were made on the embryology of Spirobranchus tricornis,. 

 Pomatostegus stellatus, and Bunice fucata (palolo). The egg of Spirobran- 

 chus tricornis shows a uniform orange color, due to pigment granules scat- 

 tered throughout the protoplasm of the egg. This pigment may be collected 

 at one pole of the egg by centrifuging, but apparently is not definitely local- 

 ized in the normal cleavage. Cleavage is equal, and gives rise to a trochophore 

 much like that of Polygordius. Attempts to carry this through the metamor- 

 phosis were unsuccessful. 



The egg of Pomatostegus stellatus has little or no pigment, and cleavage 

 is unequal. The trochophore is opaque, and rapidly metamorphoses into 

 the metameric condition, showing three sets of setae at the forty-second 

 hour. By the forty-eighth hour of development they settle to the bottom 

 and begin to form a calcareous tube. In 16 days these tubes had reached a 

 length of 3 mm. A number of these have been collected on glass plates and 

 tiles and planted on the coral reef near the laboratory, where it will be pos- 

 sible to determine their rate of growth under perfectly normal conditions. 



A few attempts were made at hybridizing these two forms. While the 

 results thus far obtained are too indefinite to be of much value, they indicate 

 that this hybridization will be possible. It is expected that researches along 

 this line will be continued in a subsequent season. 



The palolo swarmed on the mornings of July 6 and 7, the last quarter of 

 the moon falling on the night of the Qth-ioth. One specimen put in a dark 

 car on the 5th swarmed the morning of the 6th, indicating that withdrawal 

 of light for one night is not sufficient to inhibit the swarming. The egg 

 shows a well-defined ring of bright-green pigment around the animal pole 

 and a patch of pink granules at the vegetal pole, this arrangement of pig- 

 ment being as marked in the immature as in the mature egg. The green 

 pigment passes entirely into the cross and rosette cells, which in later cleav- 

 ages are prominent because of this contained pigment. The trochophore has 

 a very broad prototrochal band (covering more than three-fourths of the 

 surface), a very poorly-developed apical tuft, and a narrow paratroch. 



