EXPERIMENTS IN THE BREEDING OF CERIONS. 7 



A COMPARATIVE ANATOMICAL DISCUSSION OF THE FIVE SPECIES 

 OF CERIONS INVOLVED IN THE BREEDING EXPERIMENTS. 



It was deemed desirable that we should have some knowledge of the 

 anatomical structures of the soft parts of the 5 species of Cerions which 

 have been used in our breeding experiments. For that purpose a 

 goodly number of specim.ens of each species was carried north this 

 year, properly expanded, killed, decalcified, and the anatomical charac- 

 ters subjected to close scrutiny. In the making of these dissections 

 and drawings I have had the assistance of Dr. G. Dallas Hanna, one 

 of my students and former associates. 



The 5 species in question are the native species, Cerion incanum 

 (Binney); the specimens used for dissection came from Porgee Key; 

 Cerion uva (Linnaeus) from Curagao; Cerion crassilahris ("Shuttle- 

 worth" Sowerby) from Ballena Point, Guanica Bay, Porto Rico; 

 Cerion casahlancce Bartsch from the White House region, Andros, to 

 which we have referred as the "White House type Cerion" in the past 

 reports, and Cerion viaregis Bartsch from the King's Road, Bastian 

 Point, Andros, referred to in previous reports as the King's Road 

 type Cerion. 



Externally no differences worthy of notice excepting shell characters 

 were discovered in these 5 types. 



Tentacles and eye-stalks are developed in the manner of all Pul- 

 monates. The locomotive disk, pedal groove, and caudal mucous 

 pore are absent. The skin is covered with a series of white lines, of 

 which those radiating from the mantle collar over the propodium and 

 mesopodium are the most pronounced. These lines are crossed by 

 connecting lines which produce an irregular reticulated pattern. 

 The spaces inclosed in the meshes are dark gray to black on the top of 

 the head, lighter on the sides and on the back of the foot. The genital 

 opening is situated on the right side, beneath and slightly behind the 

 eye-stalk; its orifice is not marked externally by a distinct structure 

 or color pattern in the specimens examined. The breathing pore is 

 opposite the posterior angle of the aperture of the shell. The anus and 

 nephridiopore are on the right side and in contact with the breathing 

 pore. 



The mouth is situated at the usual position, on the ventral side of 

 the head. Immediately behind this is the broad opening to the pedal 

 cavity. The pedal cavity narrows quickly and forms part of the 

 inner floor of the body cavity as a membranous duct. 



The jaw is more or less strongly arched and provided with a median 

 projection on the concave margin. The latter is scarcely perceptible 

 in Cerion incanum and Cerion crassilahris, but is strongly marked in 

 Cerion viaregis. No vertical m^arkings were noticed in any of the 

 specimens examined and concentric lines when present are very faint. 



