641 



3) In Opsanus tau. 



The swim-bladder of the toadfish is a heart-shaped organ, deeply 

 bilobed in front by a longitudinal, vertical septum which divides only 

 the anterior half of the organ. On each side of the swim - bladder, 

 embedded in its wall, is a longitudinal band of striated muscle which 

 runs from the anterior end backward to the posterior end of the organ. 

 The fibers of the muscle bands are transverse to the long axis of the 

 swim-bladder, and are innervated by a branch of the first spinal nerve. 

 This nerve, in order to reach the swim-bladder muscle, runs from its 

 ganglion around the outside of the entire group of the spinal nerves 

 from the second to the fifth inclusive. 



The egg of the toadfish is very large, being 5 mm. or more in 

 diameter. When extruded, the eggs are cemented to the under side 

 of stones and other submerged objects. At the time of hatching, the 

 larva is about 6 mm. in length, but it remains fixed to its attachment 

 until the yolk-sac is absorbed. When this process is completed, the 

 young fish is 15 or 16 mm. long. About this time it loses its con- 

 nection with the object to which it is attached, and straightway be- 

 gins to lead an independent, free-swimming existence. 



Soon after the hatching of the larva the swim-bladder fundament 

 appears as an evagination from the dorsal side of the oesophagus, 

 just anterior to the liver duct (Fig. 8a). It grows upward through the 

 mesentery into the region bounded dorsally by the aorta and laterally 

 by the kidneys. The proximal end of this fundament remains for a 

 little time as a pneumatic duct connected with the oesophagus, while 

 its distal end swells out to form a vesicle which grows forward so that 

 the duct comes to open into its posterior end (Fig. 8b). The duct then 

 atrophies, thus leaving the swim -bladder as a simple closed vesicle 

 Fig. 8c). This is composed of cubical epithelium, and is invested with 

 a compact layer of cells which it has brought with it from the mass 

 of splanchnic mesenchyme through which it passed in the course of 

 its growth up through the mesentery. The ventral portion of this 

 laver very early becomes invaded by a branch of the coeliac axis and 

 soon becomes much thickened ; subsequently it develops the bundles of 

 capillaries which are to form the blood supply of the future red gland. 

 This splanchnic layer is the fundament of the inner portion of the wall 

 of the swim-bladder (tunica interna of the older authors ; inner and middle 

 layers; vascularis and muscularis). Shortly after the establishment of 

 the inner layers, amoeboid mesenchyme cells insinuate themselves be- 

 tween the kidney and peritoneum, and apply themselves to the out- 



Anat. Anz. Aufsätze. XXXVIII. 41 



