On the Labral Glands of a Cladoceran (Simo- 

 cephalus vetulus), with a description of its 

 mode of feeding. 



By 

 H. Graliain Caiiiioii, B.A., 



Demonstrator in Zoology, Imperial College of Science, 

 South Kensington. 



With Plates 9, 10 and 2 Text-figures. 



Leydig (12) in 1860 was the first worker to point out that 

 the possession of labral glands is common to all the Cladocera. 

 In 1846, however, Schodler (16) had observed that in the 

 labrum of Acanthocercus there exist paired glandular 

 bodies; he states, ' Im sog. Labrum (des Acanthocercus) 

 glauben wir ein paar rundliche, fast nierenformige Conglomerate 

 als driisige Korper (vielleicht als Speicheldriisen, glandulao 

 salivales) ansprechen zu miissen '. Glaus (3) in 1876 mentioned 

 these glands in his work on the anatomy of Daphnids, and 

 later Cunnington (5) in 1903 described them in Simo- 

 cephalus sima (Simocephalus vetulus). 



Among the other Phyllopoda, Claus (4) in 1886 mentions and 

 figures the glands in B r a n c h i p u s and A r t e m i a . Kef er- 

 ring to the labrum he states : ' endlich in dem terminalen 

 Theil die grossen als Speicheldriisen gedeuteten Driisenzellen, 

 deren Ausfuhrgangsoffnung und Driisenstructur auf Quer- 

 schnitten leicht zu constatieren sind '. Sars (15) states that 

 these glands exist in Limnadia and Limnetis, and in 

 his figures of other Phyllopoda large cells are indicated in the 

 interior of the labrum. 



With regard to the anatomy Claus (3) was the first to give 

 a description in any detail, but apart from this the only descrip- 

 tion at all complete is due to Cunnington in his description of 

 the glands in Simocephalus sima. Claus considered that 



