NOTES AND MEMORANDA. 419 



small. In Harpirhynchus this latter is absent, owing, apparently to 

 the mode of life of this animal, which feeds itself on the product of 

 the sebaceous glands of its host, and gets rid of the eifete gases bv 

 means of its tracheal system. 



Respiratory Organs.— The tracheae are very well developed, and 

 are made up of two principal trunks which open near the rostrum. 

 1 he stigmata have a screw-shaped form, thanks to which the entrance 

 ot toreign bodies is very effectually prevented. 



Generative Organs.~The male organ is always placed behind the 

 anus,_ where this is apparent, and the female organs occupy the same 

 position m two species ; curious as this fact appears to be, we must 

 remember that in the Hirudinea and even Annelides the position of the 

 genital orifice may vary very greatly. 



Organs of Belation.— The ai^pendages differ in even different 

 species, owing to the different modes by which the possessors are 

 connected with theii- hosts; in the genus Chyletus these variations are 

 confined to the terminal portion of the appendages ; in Harpirhynchus 

 delicate "" ^'"'''^ ""''^ ^'"'"''"^ reduced, and in Myobia they are very 



Intimate Structure of the Central Nervous System of Decapodous 

 Crustacea. -M. E. Yung describes* the neJvous system of the 

 Crustacea as composed of fibres and cells. The fibres always present 

 an envelope and contents. Contrary to the opinion of Remak, fibrillar 

 bundles are never found homologous with the cylinder-axis of the 

 nerves of Vertebrates. The fibrillar structure does not appear until 

 after the action of reagents. The contents of the cells are also 

 surrounded with an envelope, and are in all points similar to those of 

 the tubes. There is a nucleus (sometimes two) enclosing one or more 

 nucleoles, which contain in their turn nucleolules. The cells are 

 apolar, monopolar, and bipolar. They are rarely found with three pro- 

 longations. W ith reagents they behave in the same way as the fibres 

 ihe latter are, m fact, nothing but cellular prolongations. The 

 elements grouped m the commissures and the ganglia are surrounded 

 with a double envelope of connective tissue. The brain seems to be 

 formed of three pairs of ganglia. 



Functions of the Ganglionic Chain in the Decapodous Crustacea, 

 —in a note in a late number of the ' Comptes Rendus,' f M. Yung says 

 that the fuuctious of the ganglionary nervous system of the Arthro- 

 poda are still little known. He has studied them in the higher Crus- 

 tacea (lobsters, crabs, &c.), always making use of living animals and 

 having regard, m the interpretation of the results, to the influence of 

 the operation, and the circumstances under which it has taken place 

 Ihere are a number of causes of error in these experiments which 

 explain the divergences of opinion amongst previous authors and 

 wJiichare to be avoided by operating not upon one only but 'upon 

 many animals. ^ 



* 'Comptes Kencius,;ixxxviii. (1879) 240; ' Rev. Internat. Sci ,' iii 160 

 t 'Comptes Rendus,' Ixxxviii. (1879) 347. ' 



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