38 THE ENTOMOLOGIST. 



the three nerves unite into one. Under these circnmstanccs 

 Dr. Landois regards the ocelli of caterpillars as a connecting- 

 link between single and compound eyes, and proposes for 

 them the name of ' ocelli compositi.' 



JMetamorphoses of Coret/tra.—Dr. August Weissmann has 

 published, in the ' Zeitschrift,' along and interesting memoir 

 on the metamorphoses of Corethra plumicornis. The larva 

 of this fly is the beautiful transparent creature, about half an 

 inch in length, vjrhich all lovers of Natural History must have 

 watched floating horizontally among the green vegetation of 

 our clear ponds, and ready, in spite of its apparent delicacy 

 and crystalline transparency, to pounce on any little unwary 

 victim which may come within its reach. At each end of 

 the body are two kidney-shaped air-vesicles, which serve 

 partly no doubt for respiration, but partly also as floats. 

 From its extreme transparency this beautiful larva offers a 

 very favourable object for study, and Dr. Weissmann has 

 described the changes which the different organs pass 

 through. I'lie large black eye of the full-grown larva, and 

 which is also that of the imago, does not exist at birth. The 

 eye of the embryo and young larva becomes, as in many 

 Crustacea, only a secondary optical organ. In opposition to 

 the views of M. Lacaze-Duthiers, Dr. Weissmann regards the 

 external sexual organs as appendages, and not as the repre- 

 sentatives of segments. The internal sexual organs, as ap- 

 pears to be the case in all insects, are present even at birth. 

 So also are the rudiments of the tracheae, which however do 

 not contaiu, and indeed are not in a condition to contain air. 

 It is still more surprising that some even of the muscles of 

 the imago, as for instance the wing-muscles, are distinctly 

 indicated, not indeed by true muscles, but by bands of un- 

 differentiated tissue, which gradually enlarge and acquire the 

 character of true muscle. The gradual formation and en- 

 largement of the diff'erent organs is effected by an infolding 

 of tlie hypodermis or cellular layer of the skin, so that the 

 new organ does not, as in most other cases, lie inside the old 

 one, but is formed by an inverted fold of skin lying inside 

 the body. The new organs also arise in the same manner, 

 the thickening and subsequently the inversion of the skin 

 taking place beneath one of the sensitive hairs. The neuri- 

 lemma of the nerve proceeding to this hair develops itself 



