THE INSECTS. 327 



multitudes that obscured passers-by on the other side of 

 the street. 



The Ephemeridce belong to a very ancient type of 

 insects, and their fossil imprints are common, occurring 

 even in the Carboniferous system. 



Stephens says : " The insects of this family are remark- 

 able for undergoing a quadruple metamorphosis, as in 

 addition to the ordinary states of egg, larva, pupa, and 

 imago, there is an intermediate one to the last two, inas- 

 much as a sort of representative of the imago is produced 

 after the pupa, but which has to undergo a further ecdysis 

 or shedding of its skin before the true insect appears. 

 In this state the insect is capable of flying, the true 

 wings being encased in a delicate membrane, which is cast 

 off very expeditiously when sufficiently mature. In this 

 operation a slit is made in the back, through which the 

 insect forces itself, and gradually withdraws its body, 

 limbs, and wings, leaving its exudium exactly correspond- 

 ing with its previous form, excepting that portion which 

 enveloped the wings, and which is rolled up in a mass on 

 each side of the thorax." He is of opinion that the 

 popular idea that May-flies are strictly ephemeral that 

 is, live but for twenty-four hours is fallacious in most 

 respects. Owing to the atrophy of the mouth-organs 

 and the condition of the abdominal cavity, the perfect 

 insect cannot eat, and is only born for the purpose of 

 propagating its species, and he thinks certainly some of the 

 family may be able to exist for two or three daySi 



The Rev. A. E. Eaton, in his monograph on the Epheme- 

 ridce, describes them as insects with a long, soft, ten- 

 pointed, sessile abdomen, furnished at its hinder extremity 

 with either two or three many-pointed setaceous or filiform 

 tails (caudal setae), and whose body is smooth and glabrous, 

 head free, with atrophied mouth-organs, carinated epistoma, 

 short subulate antennae, composed of two short, stout joints, 

 succeeded by a slender many-pointed setaceous awn, three 

 ocelli and large oculi (compound eyes, always larger in 

 the male), thorax robust, sternum well developed. The 

 abdomen in the male is furnished with a pair of forceps 



