446 SUMMARY OF CURRENT RESEARCHES RELATING TO 



nucleus ; the contractile substance being thus absorbed, the embry- 

 onic cells increase in number, and the primitive fibre is seen to consist 

 of a perfectly homogeneous substance, with a sinuous border, the 

 depressions in which are occupied by the accumulated embryonic cells ; 

 the central part of the contractile mass is pierced with holes which are 

 likewise filled with these cells ; and, at a later stage, the place of 

 the fibres is merely indicated by a mass of proliferating embryonic 

 cells. 



h. Disajipearance of the muscle, accompanied by the degeneration 

 and death of its nuclei, — After the disappearance of the sarcolemma, 

 the centre of the still lenticular nuclei is seen to be occupied by fine 

 granulations ; these become more and more rare, till they disappear, 

 when the nucleus is merely represented by its sheath ; the contractile 

 layer meantime has been disappearing, and that so slowly and so 

 regularly that the general form of the fibre remains unaltered. The 

 final product is a colourless and very finely granular substance, in 

 Avhich are found nuclei in various stages of degeneration. 



Axis-cylinder and Peripheral Nerve-cells in relation to Sense 

 Organs in Insects.* — The nature of the nervous swelling which occurs 

 at the base of certain hairs in the Arthropoda, and of the filament 

 which terminates this swelling, has been studied by J. Kiinckel and 

 J. Gazagnaire in the Diptera. 



The swelling in question is found to be of a uniform structure 

 in all cases; it is connected by one extremity with one of the 

 ultimate nervous fibres, and by the other with an ordinary or a 

 specialized hair. The nerve-fibre from which it springs consists 

 of a neurilemma containing nucleated cells and of an axis-cylinder ; 

 the nervous swelling has a capsule composed of the dilated neuri- 

 lemmar sheath, and this expands at the base of the hair into a 

 small cup whose edges are in union with the hypoderm surround- 

 ing the chitin of this part ; into the capsule the axis-cylinder pene- 

 trates, and gradually widens out into a bipolar cell of some size, 

 provided with a nucleus and refringent nucleolus, and finely granular 

 like the axis-cylinder itself, but devoid of a cell-wall ; the distal end 

 becomes attenuated and ends in a small strongly refringent rod which 

 fits into the centre of the hair and receives external impressions from 

 it. The bipolar cell is enveloped in protoplasm which generally 

 contains a variable number, not exceeding eight, of large nucleated 

 cells ; but all stages may be observed, from that in which the bipolar 

 cell exists alone in its sheath, up to that in which it has its proto- 

 plasm and eight surrounding cells. These accessory cells appear to 

 be of the same nature as some other cells which occur in certain 

 dilatations of the neurilemma, which are especially abundant at points 

 where the axis-cylinder gives off several branches; for they are 

 similarly affected by reagents, and when but one occurs in the sheath 

 of the ganglion, it is, like those in the neurilemmar diverticula, found 

 pressed against the walls. Such is the essential structure of every 

 nervous swelling in insects which is devoted to the transmission of 



* CompfoH Rendus, xcii. (1881) pp. 471-3. 



