MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 113 



the circular, oblique, und transverse muscles. Their peculiar arrangement enables the cirrus to 

 elongate or shorten without anv undue pressure upon the central nerve. The arrangement of 

 the cirrus muscles is very similar to that in the arms of the Octopoda and Decapoda. In these 

 also there is a large, nearly central nerve, surrounded by a mass of connective tissue and trans- 

 verse muscle fibres. Around this are the longitudinal muscles, which are also arranged radially. 

 But instead of forming a complete circle, as in the cirri of Nautilus, the longitudinal muscles form 

 two to four separate masses. In its essential features, however, the arrangement is remarkably 

 similar in both the Di- and Tetra-branchiata. 



It has been mentioned that between the annular grooves of the cirrus arc comparatively wide 

 projecting ridges, which show well in a longitudinal section of a cirrus. (Fig. 50.) The ridges 

 are aiuuilar, extending completely around the cirrus. The inner portion of each annular ridge 

 projects considerablv more than the outer portions and forms an organ of adhesion. Into this 

 projecting portion great numbers of uuiscle fibres extend nearly perpendicular to the inner sur- 

 face. (Figs. 50 and 51.) The arrangement of the muscles in this region is very peculiar. Naturally 

 there are almost no longitudinal fibres present. As the transverse muscles issue from between 

 the inner longitudinal umscles they seem to branch to form an extensive Inrush, the outer ends 

 of which are applied to the basement membrane. The muscle fibres are not branched, Init are 

 so attached to one another (like the straws of a liroom to the handle) as to form a central strand 

 which passes between the longitudinal muscles. (Fig. 51, R:\I.) This strand can be traced in an 

 arc, as has been described for other transverse muscle fibres, across a portion of the cirrus till it 

 passes outward lietween longitudinal muscles. Apparently the central strand serves as a sort of 

 tendon to the radiating fibres of the inner portion of the annular ridge. These radiating fibres 

 are short and thick, and ciuite unlike those in the other portions of the ciri-us. 



As each strand forming the so-called tendon runs to an opposite portion of the cirrus the 

 contraction of all these can scarcelv take place without causing some contraction of the cirrus in 

 a transverse direction, i. e., a lengthening of the cirrus. Possibly many of the arcuate trans- 

 verse fibres share in this action. 



As the contraction of the radiating fibres within the inner portion of the ridge would pull 

 the inner face of this latter inward, a sucker is thus formed. If these suckers were applied to 

 any object the effect of the contraction of the transverse fibres in the body of the cirrus would 

 be" not to lengthen the latter, but to increase its rigidity, and thus increase the mechanical effi- 

 ciency of the^suckers along it. Any one such sucker would possess but little holding power. 

 Init thirty or more suckers upon each of thirty or more cirri must be able to hold very strongly. 

 WiLLEY says that ••most of the tentacular appendages of nautilus have essentially an adhe- 

 sive function, to which is related a prehensile function. They are employed for seizing hold of 

 food and for attachment to surfaces. Attachment is effected by the definite suctorial ridges 

 upon their lower and inner surfaces. When attached by its tentacles, nautilus holds on with 

 considerable tenacitv, and sometimes in forcibly detaching it some of the tentacles break off and 

 remain fixed to the surface of attachment." In Fig. 1. pi. 11, Q. J. M. 8. 10, AVilley repre- 

 sents a Nautilus holding to a glass vessel. 



In considering the remarkable holding power of cephalopod suckers we must remember 

 that attachment is effected under water, so that a perfect vacmmi is possible. Another condition 

 must affect the deep-sea forms like Nautilus much more, namely, that they are under a pressure 

 of 20 to 80 atmospheres, where any vacuum attachment would be immensely more powerful 



than at the surface. 



The nerve of the cirrus extends throughout its length, remaining of the same size nearly to 

 the end. It tapers slightlv here and ends abruptly immediately beneath the epithelium of the 

 tip of the cirrus. (Fig. 50.) Ganglion cells are found at the periphery of the nerve as far as it 

 runs in the cirrus. (Fig. 71 . ) Biit in regions corresponding to the annular ridges aggregations 

 of ganglion cells are found which form annular enlargements or ganglia upon the nerve. There 

 is a ganglion for each and e\ery annulus. Numerous small nerves arise from these ganglia and 

 pas.slo tlie external parts of the cirrus. Branches to the inner portions are especially numerous. 



