590 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Dytiscid®, in which its characters are very well marked, describes in 
order the apparatus as found in the German species of Cybister , 
Dytiscus, Acilius, Grapboderes , and other representatives of the family. 
B. Myriopoda. 
Ocelli of Lithobius.* — 31. Y. Willem has made a study of the ocelli 
of Lithobius forjicatus, on which Graber, Grenacher, and Sograff have 
published more or less discrepant reports ; M. Willem confirms, in the 
main, the results of Grenacher. He finds that each ocellus has the 
form of an elongated cylinder, bounded externally by the cornea, and 
enveloped by a connective membrane which is traversed by the optic 
nerve ; in the grooves which separate the corneae from one another, this 
membrane is thickened and contains a mass of small pigmented cells. 
The cavity of the eye is occupied by two kinds of cells; some, the 
Haarzellen of Grenacher, are pigmented, and separate the cornea from 
the true retina. They end internally in delicate cilia which in the 
author's sections did not exhibit the regularity ascribed to them by 
the drawings of Grenacher ; they are, rather, aggregated into irregular 
tufts. 
The base of the optical section is occupied by a score of retinal cells, 
which Grenacher was only able to detect in exceptional cases. Each 
of these has a basal segment, which incloses the nucleus, pigment granu- 
lations, and Grenacher’s rod ; this last is distinctly striated transversely. 
In a few favourable sections the author was able to detect, between the 
striated segments of adjoining cells, elongated elements which present 
the same appearance as the lateral rods of the retinal cells of the larv® 
of Acilius. Some of the author’s preparations explained the cause of 
Graber’s errors of interpretation, which he thinks due to preconceived 
notions and too thick sections. 
5. Arachnida. 
Classification of Elites. j — Prof. G. Canestrini proposes the following 
classification : — 
Order 1. 
Astigmata 
Hvdracarina .. 
Prostigmata . . 
C ryptostigmata. 
Metastigmata .. 
Mesost.gmata .. 
Class Acaboidea. 
Suborder V trmiformia. Demodicid®. Phytoptid®. 
„ Sarcoptina .. Cytoleichid®. PsoroptkUe, 
Linocoptid®. Listrophorid®, 
Dermoglyphid®, Analgesid®, 
Tyroglyphid®. 
Halacarid®, Limnocharid®. Hydraehnid®. 
Suborder Trombidina. Tarsonemid®, Cheyletid®, 
Erythr®id®, Tetranycliid®, 
Raphignathid®, Eupodid®, 
Bdcllid®, Alychid®, 
Rhynchlophid®, 
Trombidiid®. 
„ Ehlopina .. Hoplopid®. 
Oribatid®. Xothrid®, Hoplophorid®. 
Ixodid®, Argasid®. 
XicoletieUid®, Uropodid®, Zerconid®, L®laptid®, 
Gamasid®, Dermanyssid®. 
* Comptee R-:n ius. cxiii. (1891) pp. 43-5. 
t Atti R. 1st. Veneto, ii. (1891) pp. 699-725. 
