LABRAL GLANDS OF SIMOOEPHALUS 281 



owing to the veiy uncertain homologies of the various mouth 

 parts in the different classes, it is not advisahle to base a defini- 

 tion of salivary gland in this group on such considerations. 

 Hence the term salivary gland should not be extended still 

 further to include the labral glands of Simocephalus 

 V e t u 1 u s . 



South Kensington. 

 August 1921. 



Summary. 



1 . The labral glands consist of a proximal and a distal group 

 of gland-cells. 



2. The proximal group consists on each side of about twenty 

 cells. The cells possess large flat nuclei and their secretion 

 collects as intercellular vacuoles. 



3. The distal glands which are in connexion with the proximal 

 groups consist on each side of five cells — four gland-cells and 

 a duct-cell. The anterior pair of gland-cells possess large 

 spheroidal nuclei between which is an ill-defined reservoir of 

 secretion. The posterior pair have cup-shaped nuclei between 

 which is a very definite reservoir of secretion. 



4. The duct-cell is in the form of a hollow tube, one end open- 

 ing to the exterior near the tip of the lahrum and the other 

 end opening into the reservoir of secretion between the nuclei 

 of the- posterior pair of distal gland-cells. The duct-cells act 

 as ducts for the whole of the labral glands, the secretion passing 

 as vacuoles from cell to cell. 



5. The duct-cell alters the reaction of the secretion before 

 passing it to the exterior. 



6. Food particles carried in the stream which is maintained 

 by the trunk-limbs through the carapace are abstracted by 

 the gnathobases of the second trunk-limbs. 



7. There are ten setae on the gnathobase of the second 

 trunk-limb, the anterior three of which are comb-like and brush 

 the secretion of the labral glands on to the food particles as 

 they collect between the maxillae. 



