i/S Papers from tlie Marine Biological Laboratory at Tortugas. 



are found in the ccelenteron. but judging by the considerable number of 

 specimens which I have sectioned I am inclined to believe that solid food 

 is rarely ingested. One of these specimens (figs. 12-18), which was 3.5 mm. 

 long and 1.2 mm. in diameter, after fi.xation and preservation for a year 

 in alcohol, had no mouth opening, so that it could have taken no solid 

 food, but its considerable size would suggest that it must have grown a 

 good deal beyond the size of the egg. To a considerable extent this growth 

 may be due to the formation of the hollow ccelenteron and to the absorp- 

 tion of water, as Davenport showed to be the case in the early growth of the 

 tadpole, but it is possible that in this case nutriment may be received from 

 another source. In all of these larva; there are considerable numbers of 

 large round cells with dense nuclei and with yellowish-green granules in the 

 cytoplasm. These are symbiotic algre, resembling ZooxanthcUa. and it is 

 quite possible that they play an important part in the nutrition of the larvas. 

 These algae occur in both Zoanthella and Zoanthina and in both the ecto- 

 derm and endoderm, though they are more numerous in the latter layer ; 

 they also occur in the youngest larvae, with imperforate mouth, as well as in 

 the oldest ones. The fact that these larvse are found at the surface at a 

 period of the day when most pelagic larvae have settled to deeper and darker 

 levels may be associated with the metabolism of this symbiotic alga, and it 

 may be that if these larvae had been kept in acjuaria which were exposed to 

 bright sunlight the later stages in their development might have been 

 secured. 



MORPHOLOGY. 



Zoanthella. The general shape of this larva has been sufficiently de- 

 scribed already and may be seen in plate i, figs. i. la. The color is a greenish 

 or brownish yellow, mottled with darker spots, and it seems probable that 

 this general color is due, in part, to the large number of Zooxanthellcs 

 present in the body-walls. The size of the larvse varies within wide limits, 

 as Van Beneden has remarked, and the size is not in itself a measure of the 

 degree of development. My smallest specimen is 2 mm. long and 0.5 mm. 

 wide (plate 2), but it is much further developed than another specimen 3.5 

 mm. long and 1.2 mm. wide (plate 3). The largest specimen which I have 

 measured is 8 mm. long and 2 mm. wide after having been fixed and cut into 

 longitudinal sections. Many specimens were sectioned without having been 

 measured, and accurate measurements of these can not now be given, but 

 their relative sizes may be determined by the number of sections in each 

 series, since the sections are of uniform thickness ; these vary from 250 to 

 600 in number. 



In none of the larvje which I have seen is there any trace of tentacles or 

 oral papilla;. In Zooiithclla the mouth and actinopharynx is formed at a 

 relativelv late stage. In the larva, 3.5 mm. long, shown in plate 3, the 

 pharynx has just begun to invaginate and the mouth is still imperforate, 



