MUSCULAR SYSTEM. 71 



common, the whole five posterior segments could be drawn 

 back, so as to become even partly imbedded in the prosoma : 

 lateral, twisting or wriggling movements were also quite dis- 

 tinct : the three posterior segments seemed to be capable of 

 less independent movements than the anterior segments ; and 

 I observed that the more powerful flexor and extensor mus- 

 cles did not run into these three posterior segments. The 

 cirri, of course, partake of the movements of the thorax ; 

 and in watching, in an uninjured specimen, the alternate, 

 protruding, gracefullv sweeping and retracting movements 

 of the posterior pairs of cirri, it was evident that the thorax 

 was the chief agent in their movement. Besides the mus- 

 cles now mentioned, there are some immediately to be 

 noticed, which extend from within the thoracic segments to 

 within the pedicels of the cirri. 



Movements and Muscles of the Cirri. — Although the 

 cirri have not been described, it will be most convenient 

 here to treat shortly of their muscles. Each cirrus consists 

 of a pedicel, having a long basal and a short upper seg- 

 ment, supporting two multiarticulate rami. The lower 

 segment of the pedicel can be drawn forward by an adduc- 

 tor muscle, attached low clown within this segment, and 

 crossing at right angles (at least in the case of the 

 anterior cirri) the corresponding muscle, of the opposed 

 cirrus, on the central, ventral surface of the thorax. This 

 segment can also be drawn back by a muscle springing 

 from the dorso-lateral surface of the thorax, and running 

 only a little way within the segment : I am far from sure 

 that the lower segment does not possess other muscles. 

 The short upper segment of the pedicel can be moved back- 

 wards and forwards, as I saw in living specimens, indepen- 

 dently of the lower segment ; .this movement being best 

 seen in the anterior cirri, which are much more often moved 

 independently of each other than are the posterior cirri. 

 The rami are capable, I believe, of being moved backwards 

 and forwards as a whole, by the movement of the few lower 

 segments, which are generally more or less confluent. 

 They can, also, be curled up and uncurled by the combined 

 movement of each separate segment. The uncurling seems 

 to separate the two rami a little laterally. Each ramus, at 



