1902.] NATURAL SCIENCES OF PHILADELPIIIA. 107 



The gland is paired, and each half lie*, as has just been said, 

 imbedded in the tissue of the corresponding half of the large, 

 paired basilar muscle. This muscle lies in the floor of the mouth 

 and pharynx and is one of the muscles used by the animal in 

 adhering to rocks or fish. By contraction of this muscle the sali- 

 vary gland is compi'essed and its secretion thus forced out. 



In the large, adult sea lamprey the two parts of the basilar gland 

 are easily discovered by dissection, lying in the medial sides of their 

 corresponding halves of the basilar muscle. In the much smaller 

 brook lamprey, the position and structure of the basilar gland may 

 be made out by stained serial sections (figs. 9a and 96). Each half 

 of the gland is a thin-walled ovoidal sac, about 2 cm. long and 

 8 mm. in cross section, in the sea lamprey. The epithelial cells of 

 the walls are of a short columnar form, and the walls are thrown 

 into numerous irregularly arranged papillse and short folds, which 

 project into the cavity of the gland (figs. 9a and 96). 



From the medial side of the gland, a short distance back of its 

 extreme anterior end, the duct leads forward, gradually approaching 

 its fellow of the opposite side, but never meeting it, to open into 

 the mouth cavity through a small papilla. Little or no secretion 

 was seen in the gland. The posterior end of the gland is separated 

 from the first gill-sac by a distance about equal to the space occu- 

 pied by two gill-sacs. 



Fig. 9a represents a transverse section through the ventral part 

 of the body of an adult brook lamprey. The large basilar muscle 

 (b.m.) is seen on each side, between the body wall (b.tv.) below 

 and the pharynx (jihar. ) above. Imbedded in this muscle is the 

 basilar or salivary gland (b.g.) whose walls are thrown into irregu- 

 lar folds and papillte, as has been mentioned. 



Fig. 96 is anterior to 9a and is drawn under greater magnifica- 

 tion. One side only of the gland is shown, the section passing 

 through it just anterior to the opening of the duct (d. ) into the 

 gland. This figure shows that the folds in the wall of the gland 

 are formed by invaginations of irregular form and at irregular 

 intervals. The wall of the duct is of about the .same thickness as 

 that of the gland, but is not thrown into folds. The duct 

 diminishes in size somewhat as it passes forward. 



As no trace whatever of this basilar or salivary gland could be 

 found in even the oldest larvce at hand, which nuist have been very 



