230 H. GRAHAM CANNON 



the food is entangled in some substance before? it reaches the 

 moutli, and frojn the disposition of the appendages and their 

 method of working it si^erns most probable that this substance 

 is produced by the labral glands. This brings S i m o c e )) h a 1 u s 

 votulus into the sanK? category of feeders as those Gastro- 

 poda, Pelecypoda, Protochordata, and Branchiopoda whose 

 nu^thod of feeding is described by Orton (14), in which the 

 prehension of the food is brought aljout by the secretion of 

 some food-entangling substance. The nature of this substance 

 in Simocephalus is, however, peculiar. Sections of the 

 glands wer(! stained according to the method recently described 

 by Keilin (9) using thionin as a metachromatic stain for mucin. 

 The nuclei of the gland-cells stained blue while the cytoplasm 

 was ])urplish, as would occur in a mucous gland, but the secretion 

 filling the reservoir not only did not stain red, as it would do 

 if it contained mucin, but showed a pale-blue tint. Bismarck 

 brown also left the contents of the reservoir unstained. If, 

 then, the metachromasy of thionin is used as a definite method 

 for the detection of mucin, the labral glands of Simo- 

 c e p h a 1 u s v e t u 1 u s must not be described as mucous glands. 



From the quotation from Schodler's work on Acanthocercus 

 at the beginning of this paper it will be seen that he suggested 

 that the labral glands were possibly salivary glands. Claus 

 does not discuss their function but merely states : ' Die grossen 

 Zellen der Oberlippe . . . betrachte ich als Lippendriiseu '. 

 Cunnington, discussing the physiological significance of the 

 secretion from the labral glands, states that the fact that the 

 secretion Hows out in front of the mouth suggests that the 

 gland is a salivary gland. 



The term ' salivary gland ', derived as it is from vertebrate 

 and more especially human anatomy, is now unfortunately 

 used in a variety of senses in the different groups of animals. 

 In some groups a certain physiological sense is implied, while 

 in otliers the term is used only in a topographical sense. 

 Among the Arthropoda, it is not possible to find, from the 

 physiological sense, a character common to all the secretions 

 of their salivary glands, while from a morphological standpoint. 



