TOWER, PRODUCTION OF SOUND IN CERTAIN FISHES 157 



history of this partition has never been investigated. There is no difference 

 in the structure of the swim-bladder in the male and female, the intrinsic 

 muscles being present in both. It is evident that we have here anatomic- 

 ally a very different structure from that in the swim-bladder of the Scise- 

 nidse, a fact which will play a very important part in the interpretation of 

 the physiological experiments soon to be described. 



|;i Toad fish (Opsamis tau). — The swim-bladder of O'psanus (fig. 4) is 

 relatively a much smaller organ than in Prionotus. When examined ex- 

 ternally (fig. 4B), it seems to be deeply bi-lobed on the anterior half; but 

 when viewed in longitudinal section (fig. 5), it is seen that less than one 

 half of the organ is actually divided. The swim-bladder is supplied with 



■im' 



CO 



ini' 



A B 



Fig. 5. SwiM-BLADDER OF OpSANUS TAU. 



A. A specimen longitudinally bisected showing the position of the internal 



septum (s). c o, central opening of septum; i m, intrinsic muscle. 



B. Another specimen longitudinally bisected showing the variation of the 



internal septum (s) . 



the same intrinsic muscles as that of the sea-robin. The muscles arise 

 at the most anterior part of the right and left lobes respectively, and are 

 separated posteriorly by only a small tendon. The muscular tissue is 

 thick and strong, the fibres running transversely to the long diameter of 

 the swim-bladder. An internal septum divides the bladder into two parts, 

 an anterior and a posterior. The septum is perforated by a small opening, 

 which forms the only means of communication between the two cavities. 

 In the posterior cavity alone is found the blood gland. 



Most interesting is the great variation found in the position of the trans- 

 verse septum in different specimens. In some cases, the partition is fully 



