ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
31 
(3) A blood-space communicating with the body-cavity exists in the 
rectal gills. 
(4) The oxygen seems to be absorbed through the tracheal loops by 
the action of the subcuticular protoplasm only, and to be discharged from 
this into the general tracheal system. 
(5) Carbonic acid, on the contrary, appears not to be carried to the 
gills by tracheal tubes, but by the blood alone. 
(6) In any case the blood would appear to play an important part in 
the excretion of carbonic acid, and a very unimportant part in the ab- 
sorption of oxygen. 
Gizzards of Odonata.* — Dr. F. Ris has studied the structure of the 
gizzard in a large number of dragon-flies, both adult and larval. The 
primitive form, as seen in Calopteryginae, has sixteen longitudinal areas, 
eight broad and eight narrow, which bear an armature of irregularly dis- 
posed teeth. In the typical Agrioninae the areas are more complicated, 
and the spines more regular; in Pyrrhosoma minium there is greater 
elaboration and concentration. In Lestes the areas are reduced to eight, 
which are differentiated into four broad and four narrow, each with 
peculiar and specialised armature. Among Anisoptera, Gomphus and 
JEschna show a reduction or concentration to four similar areas. Finally, 
Cordulegaster and the Libellulidm differentiate the four areas to two 
pairs of teeth, so that a primitively radial arrangement has become bi- 
lateral. These conditions are clear in the larvm, but obscured in the 
imagines, where the organ tends to be reduced. The reduction is least 
in Calopteryx, much more in Agrion, most in Gomphus and JEschna. In 
Cordulegaster and the Libellulidae there is in the adult but little trace of 
the larval conditions. On the basis of his researches, the author suggests 
the following scheme of relationships : — • 
Parasitic Beetles.f — Dr. G. Brandes notices an account of the 
beaver of the Elbe by H. Friedrich, to which is appended remarks on 
Platypsyllus castoris Ritsema. The history of this insect dates back to 
1868, when it was brought before the Ashmolean Society by Westwood, 
* Zool. Jahrb. (Abth. Syst.), ix. (189G) pp. 596-621 (tigs. A-N). 
t Centralbl. f. Bakteriol. u. Parasitenk., l te Abt., xx. (1896) pp. 297-305. 
