NEMA TO CERA. 47 



brown flat chrysalis, known as a " flax-seed." The larvae of Cecids 

 do not undergo many moults, and eventually form a cocoon. 



The history of this cocoon formation, if correct, is curious. Win- 

 nertz absolutely denies that this cocoon is spun : he says it is 

 generally formed by an excretion and not by threads. He observed 

 one larva that in twenty-four hours was surrounded by a halo of 

 white thread-like particles, resembling the spicules of crystals, the 

 larva remaining motionless the whole time. There are often no signs 

 of a thread in these cocoons, which are formed in a few days. 

 Others have resinous cocoons, and some spin undoubtedly a silken 

 thread. The larval skin is not always shed during transformation. 

 This change from the larval to pupal state is marked by a change of 

 colour in the maggot, the anterior segment at the same time 

 becoming distended, and by degrees the rudiments of the wings, 

 legs, etc., become developed, and eventually the full pupal state is 

 reached. 



The pupte (Fig. 9) of the Cecidoiiiyidie resemble in some respects 

 those of Sciara, and are usually brownish flattened bodies of small 

 size, resembling seeds. The bases of the antennae are often produced 

 into points, resembling horns. Behind these horns bristle-like pro- 

 jections may be seen in most pupae — one pair on the head, and 

 another on the thorax. Spinose processes may also be developed on 

 the abdominal segments, all these processes helping the insect to 

 work its way out of the gall or earth at the time of emergence. 



The length of pupation is very variable, warmth greatly hastening 

 the development. Under unfavourable conditions the pupce may 

 remain unhatched until the next year. Those of the Hessian-fly 

 may be retarded by cold, but are not killed by a low temperature ; 

 dampness is essential to their hatching, a dry cold being injurious 

 to the "flax-seeds." 



Mention has been made of the injurious nature of the Cecido- 

 myidae. Of this there is no doubt; they, nevertheless, are beneficial 

 as vvell as injurious. By their means a great many plants are 

 fertilized ; owing to their small size they can enter plants that very 

 few insects can enter. 



No better example of the fertilization of a plant can be taken than 

 that of Aristolochia clematis^ which is largely done by Cecidomyida^. 

 I have myself seen as many as five Cecids in a single blossom of this 

 plant ; one, however, is the general rule. 



Fertilization takes place in the following way : This plant, which is 

 a protogynous dichogamous plant, belongs to the family Aristolo- 

 chiacecE, and is widely spread over the globe, several species of the 



