LABRAL GLANDS OF SIMOCEPHALUS 215 



cephalus metanauplius was fixed in cold saturated 

 sublimate and M^as found to be very well fixed. 



Ehrlich's haematoxylin was used considerably for staining. 

 Iron haematoxylin gave too intense a stain for the gland-cells. 

 The best differential stain, however, was obtained by. using 

 Mallory's triple method for connective tissue. 



The fixed material was embedded direct into paraffin and 

 cut 8 jw. 



On the Anatomy of the Labral Gi^and. 



The two groups of gland-cells, as described by Cunnington, 

 were found to be very distinct and will be described separately, 

 but before doing so the extent and position of the labrum must 

 be stated. The labrum, or upper lip, is an immediate prolonga- 

 tion backwards of the ventro-posterior part of the head, passing 

 ventrally to the two laterally-working mandibles and ending 

 under the maxillae which are immediately behind the mandibles. 

 When viewed from the ventral side it may be described as 

 dagger shaped, but its contour is peculiar and reference must 

 be made to Text-fig. 1, which is a ventral view of the animal 

 as it is seen resting normally in a watcti-glass, and to PI. 10, 

 fig. 13 which is a diagrammatic lateral view of the animal. 

 Anteriorly the labrum is marked off from the dorsal part of 

 the head by a groove on eaclx side (PI. 9, fig. 3) which extends 

 forward to the level of the nauplius eye and then expands 

 dorsally into the bay from which arises the second antenna. 



In the living animal the labral glands can be seen indistinctly 

 in the anterior part of the labrum and are of a pale-yellow 

 colour, as was observed by Ley dig (12). 



Proximal Group., — This consists of two laterally placed 

 groups of epidermal cells which almost meet in the mid-ventral 

 line between the first antennae. Each group commences just 

 in front and close to the ganglion of the nerve to the first 

 antenna (PI. 10, fig. 13), and extends postero-dorsally over 

 a lozenge-shaped area lining the lateral cuticle of the labrum 

 as far back as the labral nerve (Pis. 9 and 10, figs. 1-4 and 13). 

 Each group consists of about twenty cells, and the nuclei of these 



