Stridulation in Crustacea Decapoda. 63 



beaches it generally buries itself up to its eyes" (Stebbing, 1893, 

 from Verrill and Smith) ; Matuta seems to live under rather 

 similar conditions. The other forms, possessing either decidedly 

 stridulating organs or features interpreted as such are either 

 terrestrial [Coenobita rugosa) or amphibious or inhabiting 

 shallow water at the shore. 



Stridulating organs of types built according to the same 

 principles as in terrestrial or amphibious Crustacea are known 

 in many Insects and in some Aranese, but it is interesting that 

 the organs in really marine Decapoda are in principle similar 

 to those in terrestrial forms. {Potamon and Thalassina are left 

 out of consideration). The first thing to be noted is that the 

 organs in Decapoda exist in both sexes; scarcely any species 

 has been obser\'ed, in which only the male possesses an organ 

 absent in the female; only in Penceopsis there seems to be some 

 insignificant sexual difference in the size of the stridulating 

 area (De Man, 1911). 



With good reason Caiman writes (1909) : "In the case of 

 purely aquatic species, the function of these organs is less easy 

 to understand". But analogies can be pointed out. A good 

 number of fishes of very different families are known to produce 

 sounds ; in many forms the sound is produced by the air-bladder 

 specially adapted for that purpose, in others by the first strong 

 ray in the pectoral fins, or the anterior rays in the first dorsal 

 fin, or the first ray in the ventral fins, or by tlie praeoperculum. 

 ( Readers taking interest in this matter may be referred to the 

 excellent work by Dr. William Sorensen: Om Lydorganer hos 

 Fiske. 1884. Sorensen describes and explains the instruments, 

 but says nothing on their biological use) . A more close analogy 

 is Corixa, a genus of Hemiptera, of which several species 

 inhabit fresh water in Europe, and they stridulate ver>^ 

 well; Pelohiiis Hennanni of the family Dytiscidai may also 

 be noted. 



