ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 753 



functions of these small organs. The existence of a small accessory ganglion 

 is of some interest, for it supports the view of those histologists who believe 

 that every sensory nerve-ending is accompanied by ganglionic cells. The 

 elytra are not active organs of touch, but they possess a much greater 

 general sensibility than the ventral integument, for they contain a very rich 

 nervous plexus, and the epidermic cells are at certain points in direct con- 

 tact with the external medium. On the ventral surface tactile sensations 

 appear to be localized in the spherical wart-like projections which are found 

 on the integument, but they must not be supposed to be seats of " active 

 sensation." The subepithelial nerve-plexus is connected with nerves of 

 some size, which arise from the nerve-chain in each somite ; these nerves 

 are composed of fibrils remarkable for their delicacy. The muscular fibres, 

 and especially those which belong to the system of longitudinal muscles, 

 are remarkable for the irregularity of their forms ; some of them are com- 

 posed of two swollen extremities connected by a constriction of varying 

 length, their fibres are neither transversely nor longitudinally striated, and 

 they are irregularly cylindrical ; they appear to be entirely composed of a 

 contractile substance, which stains an orange-yellow with picrocarmine. 



The elytra of Polynoe Grubiana contains a nerve-plexus analogous to 

 that which is found in the elytra of Hermione, but the dorsal cirri differ a 

 good deal in their general structure. The tactile functions are exercised 

 chiefly by the terminal segment, and the tactile powers of the stem of the 

 cirrus, which are so well developed in Hermione, are here much reduced ; 

 the presence of a large number of large glandular cells on the basal joint 

 gives a peculiar aspect and function to these appendages. 



Chlorsema Dujardini and . Siphonostoma diplochaitos.* — M. Joyeux- 

 Laffuie cannot agree with M. Kiinstler in thinking that Ghlorsema Dujardini, 

 which attains a length of 15-20 mm., can be the same animal as Siphono- 

 stoma diplochaitos, which is about 8 cm. long. 



B. Nemathelinintlies. 



Tylenchus devastatrix.f — Herr T. Eitzema Bos gives a preliminary 

 account of the structure, habits, and practical import of the nematode 

 Tylenchus devastatrix, which is a too abundant cause of disease in rye. He 

 is about to publish a complete account of his investigations in monographic 

 form. 



The first part of his paper is occupied with a history of previous inves- 

 tigations relating to the genus Tylenchus. He reviews the various forms of 

 Tylenchus which have been described, and discusses them in relation to the 

 diseases which they occasion in numerous plants. T. devastatrix may live 

 on very different cultivated plants. Tylenchi which have been restricted 

 for generations to one kind of plant come to differ in form and size from 

 the same species on other plants. With them as with other parasites, 

 slight changes appear in response to different environment. The author 

 suggests that the free-living T. intermedius of do Man is the original species 

 of which T. devastatrix Ritzema Bos (T. dipsaci Kiihn -f T. devastatrix Kiihn 

 4- T, asTcenasyi Biitschli + T. hyacinthi Prillieux -f- T. Lavensteinii Kiihn 

 -{- T. alii Beyerinck) is only an adaptive modification. 



T. devastatrix inhabits only stems and leaves, never roots. It infests 

 certain plants specially (rye, onions, hyacinths, teasel, &c.), and causes 

 disease. It occurs in many others, but without doing much damage. It 

 has been recorded in 34 species, representing 14 different families of plants. 



* Comptes Rendus, cvi. (1887) pp. 179-80. t Biol. Centralbl., vii. (1887) pp. 232-43. 



