645 



Huot ('02) described the embryonic swim-bladder of Lophobranchs 

 as a simple vesicle, at the posterior end of which the pneumatic duct 

 is attached. He mentions the duct as soon disappearing, but he did 

 not trace its later fate in detail. In the case of Syngnathus, according 

 to Baglioni ('08), the swim -bladder is directly connected with the 

 anus by a "pneumatic duct". Nothing is known of the later stages 

 in the ontogeny of this species, but it may be conjectured that the 

 vestigial limb of the duct grows downward and acquires a secondary 

 connection with the intestine. 



5) In Tautogolabrus and Tautoga onitis. 



In both these species the posterior chamber develops directly 

 from the embryonic pneumatic duct in essentially the same manner 

 as in Siphostoma. 



6) In Urophycis and Stenotomus chrysops. 



In a 4 mm. specimen which I identified as probably belonging to 

 a species of Urophycis, the swim-bladder is already a large and well 

 expanded organ. Its pneumatic duct has begun to atrophy, but it is 

 still connected with the oesophagus, and can be followed around to 

 the posterior end of the swim-bladder. 



In specimens of Stenotomus chrysops about 3 mm. in length, the 

 lumen of the swim - bladder, toward its posterior end, becomes con- 

 tracted into a tube which turns somewhat to the left of the median 

 line, then extends backward a short distance and ends blindly. At 

 the posterior end, the epithelial lining is continuous with a solid cord 

 of cells which bends around to the left and runs forward a slight dis- 

 tance in the wall of the swim - bladder. In some cases this can be 

 traced through the mesentery into the splanchnic layer of the intestine. 

 This cord of cells I interpret as being the remains of the pneumatic 

 duct which has undergone a considerable degree of atrophy. In a 

 specimen 4,5 mm. in length the swim -bladder appears to be divided 

 into an anterior and a posterior chamber which seem to be connected 

 by means of a very small tube. 



The swim - bladders of Urophycis and Stenotomus belong to that 

 type of the organ in which an oval is found. Up to the present time, 

 so far as I am aware, no information regarding the development of 

 the oval exists in the literature. The isolated stages described above 

 are, of course, not in themselves a sufficient basis for generalization, 

 and it can only be said that they tend to corroborate the morpho- 

 logical theory which will be stated immediately. But whatever future 

 investigation may show when it has become possible to secure the 

 proper material for the study of the ontogeny of the oval, it seems 

 justifiable at present to say that the swim-bladders of these two genera 



