118 SUMMARY OF CUEEENT RESEARCHES RELATING TO 



goes remarkable changes rapidly and snddenly at the last moult. A 

 description is given of the main tracheal system : the first three spiracles 

 closed but functional in the adult (the second and third turned dorsally) ; 

 the closed spiracles (fourth, fifth, nineteenth), \vhich are entirely absent 

 m the adult ; the sieve-plate spiracles (sixth, seventh, eighth) ; the 

 last segment of the abdomen ; the anal siphon ; the last spiracle — the 

 only open one in the adult ; and the respiratory structures in the thorax 

 of the adult. 



The adult breathe the atmospheric air. This is ordinarily taken in 

 by the anal siphon, and through the siphonal spiracles it enters the main 

 trachael trunks and their branches. The insect also keeps a supply of 

 air under the ^uugs and in the concavity of the mesothoracic pleuron. 

 The respiratory system is a closed system of tubes with numerous 

 ramifications with only two openings, viz. the last pair of spiracles at 

 the base of the anal siphon. Of the rest of the system in the adult, 

 only three small membranous surfaces— spiracles one, two, and three — 

 can be in contact with the air. Under these given circumstances one 

 inference is possible — the respiration is carried on by the diffusion of 

 gases through the membranous covering of the thoracic spiracles. 



In the nymph there are ten pairs of spiracles — all ventral, all open, 

 and functional. There is no siphon, but there is a short concave 

 projection from the abdomen instead. In this and in the two shallow 

 grooves on either side of the raised mid-ventral region of the abdomen 

 there is always a layer of air, collected at the surface and retained by a 

 coveriug of hairs. Atmospheric air is essential to the nymph. The 

 reasons for the change from the nymph respiratory arrangements to 

 those of the adult may be that the exigencies of reproduction imply 

 prolonged submersion, and that the insect during winter may have to 

 remain a long time under a layer of ice. 



Comparative Study of Chromosomes.* — Browne has studied the 

 chromosomes in sis species of Notonecta, and finds no definite correla- 

 tion between the somatic and the chromosomic characters, except that 

 the 14-chromosome species are the smaller, and the 13-chromosome 

 species the larger. Each species has indeed a definite number and 

 arrangement of chromosomes, but the status of a species in relation to 

 its neighbours cannot yet be determined on this basis. 



G-enera and Species of Mallophaga.t — Launcelot Harrison has 

 made a list of species of Mallophaga included in the genera Pedmdus 

 Linn, Ricinus Degeer, and Nirmus Hermann ; a list of generic and 

 sub-generic names, valid and invalid, used for Mallophaga ; a provisional 

 scheme of classification ; a list of species and sub-species, valid and 

 invalid, of Mallophaga. Of specific names, 1520 are treated as valid, 

 and 875 as invalid. This list of the systematic nomenclature of the 

 group will be of great value to investigators of Mallophaga. 



* Journ. Morphology, xxvii. (1916) pp. 119-62. Sea also Trans. Arner . Micr. 

 Sec, XXXV. (1916) pp. 141-2. 



t Parasitology, ix. (1916) pp. 1-156. 



