256 



IWAJI IKEDA. 



The curious phenomenon took place also in the two following mornings. 

 It should here be noted that the individuals swam in every direction, but 

 were probably blown together into zones by winds and carried away en 

 masse by tidal currents. 



To the above observations the informations gathered from fishermen 

 may be added. They call this Balanoglossus " Binbo-mushi " (Pauper 

 worm). The swarming on the surface should take place on calm nights dur- 

 ing summer months, from August to the beginning of September (not every 

 year, but often with an intermission of several years). The floating animals 

 are said to be especially lively for some hours before daybreak. They 

 should usually live on the bottom of from five to fifteen fathoms. 



It is certain that our swimming Balanoglossus is Glandiccps Jiacksii, 

 first described by Marion, then by Spengel and recently by Menon.* It is 

 noteworthy that, as pointed out by the last author, the post-hepatic region 

 of the species is extremely flattened, and while swimming both the lateral 

 expansions function as fins. Another point should be noted is the 

 decided difference in coloration between the dorsal and ventral sides. 

 This suggests the fact that the animal lies flat on the bottom, dark dorsal 

 face up. This premise was proved to be correct when the stranded speci- 

 mens were examined. From the two characteristics it may not be amiss 

 to conclude that this species is a swimmer as well as a creeper, but not a 

 burrower as other Enteropneusts are. This conclusion is also strengthened 

 by the fact that no sands are found in the digestive tract, the food con- 

 sisting entirely in micro-orgainsms such as diatoms, and dinoflagellates.** 



As to why this Balanoglossus comes up to the surface at certain 

 period, I am unable to answer. At first I thought that this might be 

 a phenomenon similar to that which takes place in certain other animals, 

 but I have come to doubt the similarity, since in the present case the swarm- 

 ing has nothing to do with sexual maturity. It is quite possible on the 

 other hand that this form comes up to the surface after microplankton, which 



• Menon, K. R., '03. — Enterepneusta from Madras : Quart. Journ. Micr. Sci. 47. 

 ** The food ingested becomes compact masses and gives the hepatic region a deep brownish 

 black color. 



