EXPERIMENTS IN THE BREEDING OF CERIONS. 13 



Each buccal ganglion is situated adjacent to the attachment of the 

 esophagus and the commissure passes beneath this over the buccal 

 retractor muscle. The cerebro-pleural and pedal commissures arise 

 on the ventral side of the cerebral ganglia. In some of the species 

 they are united for a portion of their length, but in Cerion crassilabris 

 and Cerion viaregis they are free throughout. The cerebral pleural 

 commissure lies posterior to the pedal commissure. In some of the 

 species nerves are found arising from the cerebral pleural commissures 

 which pass to the right and left cephalic retractor muscles. 



The pleural elements are asymmetrical, a greater development being 

 present on the left side. There are five ganglia in all, two on the right 

 side and three on the left. From the upper two, pleural pedal com- 

 missures pass forward to the pedal ganglia. In Cerion incanum, 

 Cerion uva, and Cerion casaUancce these nerves are so short as to be 

 scarcely discernible. The two true pleural ganglia are the largest of 

 the series, the left being slightly the larger of the two. From the right 

 one a large nerve arises and passes to the mantle collar, while two large 

 nerves pass from the left to the floor of the pulmonary cavity. Between 

 the left pleural and the upper pleural there is an extra ganglion which 

 may correspond to the abdominal ganglion of certain other mollusks. 

 At all events, it gives rise to a large nerve which passes to the viscera. 

 The two pedal ganglia lie just in front of the pleural ganglia and are 

 practically of equal size and shape. They join indirectly without a 

 commissure. Numerous nerves pass from these to the tissues of the 

 foot, especially in the anterior region. 



A very distinct blood-vessel passes between the pleural and pedal 

 elements, which connects the base of the buccal mass with the wall of 

 the mantle covering the visceral mass. It then passes backward beneath 

 the pulmonary cavity, being free throughout most of its length. 



The great diversity in the anatomical structure of the five species 

 of Cerions examined might tempt one to generalization, but I believe 

 that it is well to postpone this until a much larger series of species has 

 been examined. It will then be easier to judge what values are to be 

 assigned to the various structural differentiations observed in Cerions. 



THE COLONIES INTRODUCED INTO THE FLORIDA KEYS. 



We will take these up under the various species involved and discuss 

 the colonies under each in serial rotation from north to south, i. e., 

 from the Biscayne Bay region to the Dry Tortugas. 



CERION VIAREGIS BARTSCH. 



Of this species, 100 specimens have been taken at random from a 

 lot of Bahama material collected along King's Road, Bastian Point, 

 Andros. These yield the measurements given in table 1 ; figures of them 



