Mr. C. P. Sigerfoos on the Pholadidse. 255 



slit appears ventral to the first, so that each filament is sepa- 

 rated from its fellows by double slits. That last formed 

 corresponds to the space between the ascending limbs of 

 adjacent filaments. The first ten filaments, then, have no 

 ascending limbs. Deshayes described * a series of plications 

 in the anterior part of the body, and thought them to be 

 normal structures. These are the first ten filaments formed, 

 which have later become separated from their fellows poste- 

 riorly by a great distance, as follows : — When the young 

 Teredo is somewhat less than 1 centim. long each gill con- 

 sists of a long series of about seventy-five filaments, stretching 

 uniformly from the anterior part of the body to the small 

 filaments which have just been formed. But now the ninth 

 or tenth filament broadens (grows in line of the antero- 

 posterior axis of the animal) till in large specimens of the 

 adult the anterior filaments may be separated from the poste- 

 rior part of the gill by 10 centim. or more. The ciliated 

 furrow described by Deshayes connects the two portions. 

 The epibranchial cavity persists as a long canal between the 

 two parts. Fusions between adjacent filaments of the first 

 fen take place, so as to more or less obliterate the gill-slits. 



Contrary to the statement of Quatrefages, there is a single 

 gill (a half ctenidium in modern usage) on either side. This 

 is the internal gill, and the external has wholly disappeared. 



Closely associated with the gill is a very prominent gland- 

 ular structure peculiar to the ship- worms. Deshayes described 

 a special gland in the umbonal region, and surmised its 

 function to the formation of a secretion for softening wood by 

 chemical action. Grobben f did not find it, and questioned 

 its existence. Deshayes also described mucus-glands in the 

 gills, whose secretion he supposed to be for the nutrition of 

 the embryos in these viviparous forms. Both are parts of 

 the same organ. In the newly attached larva there is a con- 

 siderable glandular structure on either side in the anterior 

 part of the body, whose duct opens under the cerebral ganglion 

 in front of the mouth. As the animal grows the gland grows 

 posteriorly, sending branches into the gill-filaments. As the 

 two parts of the gill become separated, the two parts of the 

 gland remain connected by a long narrow (? functionless) 

 duct, which accompanies the epibranchial canal. Further 

 than this 1 am at present unable to describe this organ, which 

 is very difficult to study. Since in this species, which does 

 not retain its embryos, the posterior part is present in young 



* ' Histoire naturelle des Mollusques.' 



t Arbeiten Zool. Inst. Wieu, Bd. vii. (188G). 



