450 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Spiders in Relation to Forestry.* — M. C. Keller ascribes con- 

 siderable importance to the influence of spiders on vegetation. The 

 first case taken up is that of their relations to Lecanium racemosum, 

 this is succeeded by that of Chermes coccineiis, where larvro have great 

 influence in the production of galls ; Chermes viridis, which appears 

 to the author to be a distinct species, is also affected by spiders. 

 After giving some other instances Keller has a systematic list of the 

 Phalangida), and of the true spiders which are important to foresters ; 

 here are included Phalangium parictinum, Opilio saxatilis, Tlierid'mm 

 lineatuin, irroratum, and varians, Agelena labyrinthica, Thomisua 

 calycinus and T. pini. 



(. Crustacea. 



Optic Ganglion of Palinunis vulgaris, f — M. H. Viallanes 

 describes the optic ganglion as being very complex in structure, and 

 consisting of the layer of post-retinal fibres, the ganglionic layer, the 

 external chiasma, the external medullary mass, the internal chiasma, 

 the internal and the terminal medullary mass. 



The ganglionic layer is remarkable for having the large nerve- 

 cells, which are numerous in the crayfish, extremely rare and 

 scattered. Some of the fibres of the chiasma have a peculiar course, 

 and each fibre swells out into a large unipolar cell ; united they 

 form a largo lobule, which is situated in front of the external 

 medullary mass ; this last has such a form that its long axis lies per- 

 pendicularly to the long diameter of the other curved parts of the 

 optic apparatus ; it is entirely made up of dotted substance. With it 

 there is connected an important ganglionic centre, which, from its 

 form, may be called the ganglionic crown ; it is formed of a number 

 of unipolar nerve-cells of various sizes, each of which gives off a pro- 

 cess w^hich passes into the midst of the fibres of the chiasma. A 

 bundle of fibres of the internal chiasma divides into two groups, one 

 of which passes into the internal medullary mass, while the other 

 joins and fuses with the optic nerve. The internal medullary mass is 

 invested internally by a ganglionic cortex, which has the same 

 function with regard to it as has the ganglionic crown in relation to 

 the external medullary mass. The terminal medullary mass is the 

 largest and most complicated part of the optic ganglion ; it is divided 

 into two parts or balls, into the superior of which the optic nerve 

 enters, and with the dotted substance of which its fibres fuse. This 

 terminal mass is almost entirely covered by a cortex formed of 

 unipolar nerve-cells, divided into a number of lobules. Each of these 

 gives off a number of fibrils which penetrate the mass, and go either 

 to the superior or the inferior ball. The sclerotic is formed by the 

 neurilemma of the optic nerve. 



Isopoda of the ' Willem Barents ' Expedition.:}: — Dr. M. Weber 

 reports on the Isopoda collected in the Arctic Seas by the ' Willem 

 Barents.' In all, fifteen species were collected during the expedition. 



* Rec. Zool. Suisse, ii. (1885) pp. 149-88 (1 pi.). 



t Ann. Sci. Nat.— Zool., xvii. (1884) Art. No. 3, 74 pp. (5 pis.). 



X Bijdr. tut de Dierkunde, x. (1884) 39 pp. (3 pis.). 



