THE PUPAL STAGE OF CULEX. 21 



length to the seventh segment. During the first two days of pupal 

 life these connectives vanish completely, and the ganglia migrate to 

 the anterior part of the seventh segment to fuse with the ganglia 

 of that segment. As Avith other composite ganglionic masses, the 

 composite nature of the ganglionic mass so formed is easily recognised 

 in sections, especially horizontal sections, even in the imago. In the 

 female the process goes a stage further. A pupa almost ready to 

 burst and give exit to the imago has still the arrangement just 

 described, but the imago, killed immediately after its escape, is 

 found to have no ganglia in the seventh or eighth segment, but in 

 the sixth segment are two masses ; the first, the pair properly 

 belonging to the segment, lying at its anterior end ; the other, the 

 double ganglionic mass formed by the fusion of the seventh and 

 eighth ganglia, lying at the hinder end of the segment. 



In the male imago, however, the arrangement is the same as in 

 the advanced pupa. 



A detailed description of the ganglia of the head and the changes 

 they undergo during pupal life would take me too far. The most 

 striking change is the very great increase in size which these ganglia 

 undergo, and the most interesting point is the way in which this 

 increase is brought about. The epidermal (" hypodermal ") cells, 

 especially those near the borders of the eyes, proliferate freely, and 

 the cells budded off from their inner surfaces migrate inwards and 

 form the new cells of the ganglia. By this process the ganglia, which 

 at the beginning of pupal life were comparatively inconspicuous, 

 grow till they almost fill the head, and there are places in the 

 advanced pupa where the ganglia and the epidermis appear to be 

 continuous. 



The sense-organs of the pupa itself are not of special interest, 

 that is, the organs which serve during pupal life as sense-organs. 

 The setm have already been mentioned. The ocelli are those of the 

 larva, but they persist to the adult condition, the chief change 

 which they undergo being the development of an exceedingly dense 

 pigment. I have already referred to the common but erroneous 

 statement that the imago is devoid of ocelli. 



The compound eyes belong properly to the imago, not to the pupa, 

 though they are probably sensitive to light in the pupal condition. 

 At first they are small (see Fig. 1) and devoid of corneal facets, but 



