184 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tion of the oral valve of the zooecium, and he shows that the leading 

 stages exist in Schizoporella ciliata. Sometimes a moderately short 

 avicularium of the ordinary type occurs ; in other cases the mandible 

 is more or less prolonged into a straight and slender spine. In speci- 

 mens from the Queen Charlotte Islands the mandible has altogether 

 lost its lid-like character and is now a very tall membrano-chitinous 

 appendage, commonly exceeding in length the entire cell ; from Ceylon 

 or Bass's Straits still another form is known, in which the spinous 

 process of the avicularium is furnished on each side with a delicate 

 membranous expansion. 



It is suggested that in the avicularian appendages is to be found 

 a ready adaptability to change of circumstances, and Mr. Hincks 

 considers that these observations bring out very forcibly the insta- 

 bility of the avicularian structure, so that he cannot agree with those 

 who assign a high value to the appendicular organs for the purposes 

 of classification. 



Arthropoda. 

 a. Insecta. 



Flight of Insects.* — E. von Lendenfeld, after some general con- 

 siderations on locomotor organs, points out that insects with one pair 

 of wings appear to be the most highly organized and possess the 

 largest brain. Before the Jurassic period no two-winged insects seem 

 to have existed ; these later ones would appear to have been derived 

 from the four- winged forms. The " dipterous " type seems to have 

 been developed along two different lines ; while in the Lepidoptera 

 Ehopalocera the anterior wings are the larger, in the Orthoptera 

 genuina the hinder are the larger ; allied to the former are the 

 Sphingidae and the Hymenoptera with the anterior wings much 

 the larger, and they culminate in the true Diptera in which the 

 anterior wings are alone developed. On the other hand, the Ortho- 

 pterous form leads through the Coleoptera, where the anterior wings 

 form elytra, to the Strepsiptera, in which the anterior wings are 

 aborted ; lower than all these are the Neuroptera planipennia and 

 the Libellulidae in which both pairs of wings are equal in size. 

 In discussing the question of the homology of the wings, the author 

 states that his own observations incline him to the view of Fritz 

 Miiller that they are derived from lateral processes of the dorsal 

 plates of the wings on which they are found, and that they are not 

 modified tracheal gills. 



The rest of the paper deals in detail with the characters presented 

 by the LibellulidsB. A diaphragm of chitin separates the muscles 

 for the wings from those for the legs ; the exoskeleton is made up of 

 a number of thin chitinous plates ; there are various methods of 

 articulation, some of which are exactly comparable to those that are 

 found in the Yertebrata. Sixty-two separate skeletal parts are named 

 and described. The wings are not only similar in structure but in 

 action and function ; the quantity of blood which makes its way into 



* SB. Akad. Wiss. Wieu, Ixxxiii. (1881) pp. 289-376 (7 pis.)- 



