BDELLOSTOMA DOM BEY L LAC. I3I 



S-shapcd figure. A slight disturbance or an internal irritation 

 will cause them to uncoil slightly, when, like a delicate watch- 

 spring, they recoil and vibrate for an instant before coming 

 back to rest (Fig. 3, a and /;). This motion is one of the most 

 beautiful illustrations of muscular elasticity which I have ever 

 seen. As shown in the Fig. 3, Bdellostoma can curve its body 

 into very complicated figures, the most complex being the 

 double and triple knots into which the fish can quickly tie 

 itself for the purpose of removing anything attached to the 

 surface of its body. This it accomplishes by keeping its body 

 in motion through the knot, and tying up as fast as it comes 

 untied. When in a position of complete rest, the fish rests 

 equally well with only a slight bend in the head or the tail 

 region, though it is the tail that is normally used as a support 

 for the body to lean upon. When irritated the fish discharges 

 from a series of minute holes in the skin, running along either 



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Xanque muscles ^""^^^^^S^^R^gl^ 



Fig. I.— The Cephalo-Branchial region of Bdellostoma dombeyi seen from 

 the left side to show the truncated anterior end of the body and its complement 

 of feelers. The position of the eye-spot and the mutual relations of the external 

 branchial pores and the thread gland pores is also given, X natural size. 



side of the body, which project like minute nipples above the 

 surface of the skin, a milky-white fluid, which almost instantly 

 disappears from sight when the fish is in the water. These 

 holes arc the openings into the so-called mucous sacs or, as 

 I shall designate them hereafter, the thread cell pockets or 

 nidamental organs. These sacs are imbedded in the muscles 

 of the body, and not in the subcutaneous tissue, as Jackson 

 affirms in his recent edition of Rollcston. The discharge is in 

 the form of minute jets, and is caused for the most part by 

 the muscular contraction of the skin about the body. The 

 fluid is composed of minute bodies about the size and having 

 something of the appearance of starch grains. Each grain is 

 a thread cell, and was originally a columnar cell, derived from 



