250 THE AMERICAN MONTHLY [November, 



Adjunct Organs to Spiracles. 



By EDWARD GRAY, M. D., 



BENICIA. CALIFORNIA. 



Upon a slide of a " potato worm/' which has very hitely been added 

 to my collection there are some curious and remarkable structures ot 

 which little notice has thus far been taken ; at any rate, the only account 

 of anything similar known to me is contained in Science Gossip oi\^%\. 

 year. These two structures are in the vicinity of the spiracle, and the 

 smaller is in intimate relation with it. The spiracle itself has a double 

 opening of long elliptical shape ; the border, strongly marked by its 

 color, has transverse markings something like the diatom cocconema. 

 Lying against the broader end is a structure resembling the halter of a 

 blowfly. As shown upon the slide mentioned, which is an ordinary- 

 balsam mount, it consists of a spheroidal sac, the walls of which are 

 thrown into a few faint, shallow folds away from the spiracle, and con- 

 nected with this a curved tube ending in a trumpet or funnel-shaped 

 oval opening traversed by several digitate lines. This terminal expan- 

 sion has but slight color and is perfectly transparent, as is also the glob- 

 ular sac at its commencement. The slide does not show wdiat relation 

 any portion of this structure may have to the trachea. This is imfor- 

 tunate for the sake of clear description. The stalked organ written of 

 in Science Gossip is presumably of similar nature, but certainly dif- 

 ferent in shape and anatomical arrangement. 



Now, what is this organ? Standing in intimate relation with the 

 spiracle it must have something to do with vibi'ations of the air, or as 

 a reservoir of some character. Whether it is a sound-producing organ 

 or a sound-registering apparatus, or neitiier, and connected with some 

 other sense, remains to be seen. In the object no tiace of nerves is to 

 be found ; but that is doubtless due to the method of preparation em- 

 ployed. Had, for example, this larva been mounted fresh in Thwaite's 

 fluid it would be practicable to determine with some approach to accu- 

 racy many points now unattainable. The structure is such that it un- 

 avoidably reminds one of the ear ; and they may be organs of hearing. 

 It can by no means be held as conclusive against this view that audi- 

 tory organs of several pairs in this region are not yet known. Before 

 it became known that certain Orthoptera carry tympana in their fore- 

 legs, any one suggesting the possibility of such an event would surely 

 have been ridiculed. It is not overlooked tliat these organs may belong 

 to a sense in the insect of which we have no knowledge. Here the 

 lack of like preparations and even the knowledge of the name of the 

 creature which furnished this noteworthy siide bars the writer from in- 

 stituting a seaiching investigation of this structure. It might be sup- 

 posed that the sac originally contained otoliths, a few bodies looking 

 like such remaining upon the slide after all the handling. 



The other structure is far more evident and less complex. It is upon, 

 or in, the chitine, and is a rather large and broad shield, shaped like 

 the half of a pear, bearing ten to thirteen transverse bands of dark color, 

 alternating with light stripes and with a row of dots in the centre of the 

 band (the former seat of hairs .^). These occur in pairs upon each seg- 

 ment of the abdomen, and very near the organs before described. It 

 is plain that the occurrence of these two peculiarities in the same crea- 



