THE PUPAE OF WEST AFRICAN MOSQUITOS. 91 



alveolar-structured organ possibly functioning as a primitive lung ; the trumpets 

 have an exceedingly narrow slit-like opening distally and the proximal ends are 

 connected with well marked tracheae, which narrow at their junction with the trum- 

 pets and become broader and more convoluted as they are traced into the interior 

 of the pupal case. Miall (Aquatic Insects, p. 119) states that " The pupa floats in an 

 upright position at the surface of the water." This statement is incorrect so far as 

 the pupa of Chaoborus ceratopogones is concerned, as it appeared to spend the whole 

 of its time at the bottom of the water in the glass vessel wherein it was placed. 

 The pupal stage lasted about 36 hours in the two specimens bred. 



In conclusion, we desire to express our thanks to Dr. Guy A. K. Marshall, 

 Director of the Imperial Bureau of Entomology, for his kind assistance in deter- 

 mining several of the species here dealt with ; and to Miss Rhodes for the great 

 care and trouble she has taken in the preparation of the illustrations. 



