MARINE ANIMALS THAT STING 61 



2. Myliobatid type (Fig. 32, Next to Top) . This type is found in 

 the bat, or eagle rays (Myliobatis, Aetobatis Rhinoptera). Their 

 tails terminate in a long whip-like appendage. The sting in these 

 rays are frequently large and well-developed, but situated near the 

 base of the tail. Under the proper circumstances these rays can use 

 their venom organs to good advantage. 



3. Dasyatid type (Fig. 32, Next to Bottom). This type is found 

 in the stingrays, proper, (Dasyatis and Potamotrygon) . The sting 

 is well-developed as in the previous type, but is frequently located 

 out further from the base of the tail, making it a more effective 

 striking organ. Stingrays possessing this type of venom apparatus 

 are among the most dangerous kinds known. Their tails terminate 

 in a long, whip-like appendage. 



4. Urolophid type (Fig. 32, Bottom). This type is found among 

 the round stingrays (Urolophus) . The caudal appendage to which 

 the sting is attached is short, muscular, and well-developed. Urol- 

 ophid rays are also dangerous to man. 



In general, the venom apparatus of stingrays consists of the ser- 

 rate spine and an enveloping sheath of skin. Together they are 

 termed the sting. Stingrays usually possess only a single spine at 

 a time, but it is not unusual to find a specimen with two or more. 

 Apparently, the spine remains until it is removed by injury. There 

 is no evidence to support the idea that they are shed each year. As 

 the young spine grows out from the tail, it takes with it a layer of 

 skin, the so-called integumentary sheath, which continues to sheathe 

 the spine until it is removed by injury or wear. 



The spine is composed of a hard, bone-like material, called vaso- 

 dentine. Along either side of the spine are a series of sharp re- 

 curved teeth. The spine is marked by a number of irregular, 

 shallow furrows which run almost the length of the spine. Along 

 either edge, on the underside of the spine, there will be found a 

 deep groove; these are technically termed the ventrolateral-gland- 

 ular grooves. If these grooves are carefully examined, it will be 

 observed that they contain a strip of soft, spongy, grayish tissue 

 extending throughout the length of the grooves. The bulk of the 

 venom is produced by this tissue in the grooves, although lesser 

 amounts are believed to be produced by other portions of the in- 

 tegumentary sheath, and in certain specialized areas of the skin on 

 the tail which lies adjacent to the spine. These grooves serve to 

 protect the soft delicate glandular tissue which lies within them, 

 and even though all of the integumentary sheath may be worn 

 away, the venom-producing tissue continues to remain within these 



