Cole (1942) using Butish Urosalpux, conducted laboratory studies at Conway 

 ot the rate of movement of the drill in a wooden trough filled with sea water , He 

 found that individual drills varied considerably in the degree and rate of movement. 

 The maximum rate (observed or.ly once) was 3 cm./min. at 14. 4° C. The maximum 

 rate in the majority of experiments ranged from 1.17 to L 75 cm./min. at all 

 temperatures from 13 to 23° C. 



Drilling and Feeding Organs 



The oyster drill and similar predatory gastropods possess a feeding 

 mechanism which exhibits a singular specialization of the muscular, nervous, and 

 vascular systems ir the proboscis and accessory proboscis in the direction of 

 unusual adaptation to predation of specific prey, The effectiveness of this mech- 

 anism is amply attested by the wholesale depredations of young oysters on commercial 

 grounds within its range . 



The mouth parts of the drill are contained, not in the head region as in the 

 majority of bilateral animals, but withir the distal end of a long muscular tube, 

 the proboscis, which consists ir part of a modified extension of the ectoderm of 

 the cephalic region (see plates 3 3 4, and 8, _m Carriker, 1943). The walls of the 

 proboscis consist of an outer mucous secreting epithelium, and four thin layers 

 of muscle, closely interwoven to form a tough pliart organ. This tube is capable 

 of movement in all planes In retraction the base of the proboscis is diawn in 

 first ard the tip follows last. The outer tip of the proboscis bears a heavily in- 

 nervated tactile rim, inside of which lies the true mouth This opens mto the 

 buccal mass, a complicated muscular bulb which contains the tooth-studded radula. 

 When fully everted the proboscis in a dull 35 mm, high measures 35 to 40 mm. in 

 length, and the buccal mass in the tip measures 5 mm. in length, 2 mm. in width, 

 and 1 .5 mm. in height. In the posterior half of the buccal mass lies a fleshy 

 tongue -like cushion, the odontophore, which supports the radula A buccal cavity 

 lies over the radula, and connects the mouth with the opening to the esophagus 

 above and behind the radula. The latter consists of a uniform cylindiical trans- 

 lucent tube which passes backward from the buccal mass through the proboscis ard 

 the cephalic cavities to the stomach. The radula consists of a long i arrow chitinous 

 ribbon armed with three longitudinal rows of sharp hard teeth which point backward. 

 Much of the radula is housed in a blind tube behind the buccal mass in the proboscis 

 cavity and gradually grows forward out of this over the odortophoral cushion . The 

 teeth are formed in this tube, and as the radula grows anteriorly the outer worn 

 teeth ar 2 lost, probably swallowed, and replaced by new teeth . Chemical tests with 

 acids show that silica is not present in the teeth in sufficient quantity to preserve 

 their form in boiling concentrated sulphuric acid; rigidity of the teeth, as in other 

 snails, probably results from impregnation with other ir organic compounds. 



22 



