MUSCULAR SYSTEM. 69 



space of body between the basal margin of the labrum and 

 the adductor muscle. This movement I saw in living spe- 

 cimens. The last and fifth pair of muscles is small, but of 

 considerable length ; it is a diverging pair, attached at the 

 converging end, above and exteriorly to the adductor muscle; 

 and at the diverging end, low down on the under side of 

 the scuta ; I am very doubtful regarding the function of 

 this pair. Altogether we have seen that round and within 

 the fleshy pedicel, by which the body is attached to the 

 scuta, there are no less than eight pairs of muscles. The 

 central space between these muscles is hollow, and here 

 many lacunal channels seem to converge. These muscles 

 receive nerves from the supra-cesophageal ganglions. The 

 interspace above alluded to, between the basal edge of 

 the labrum and the adductor scutorum muscle, occupies a 

 very different position according as the animal's body is 

 protruded as far as it can be, or is retracted. It is homo- 

 logically part of the third cephalic segment ; and conse- 

 quently the mouth ought to have stood posteriorly (i. e. 

 above, in the position figured in PI. 25, fig. 1) to this inter- 

 space; yet, in fact, when the animal is retracted within 

 its shell, the mouth usually lies almost directly beneath this 

 interspace and the adductor scutorum muscle. 



Besides these muscles of attachment, the prosoma is fur- 

 nished with several other muscles. There are superficial 

 muscles running up towards the basal margin of the sides 

 of the mouth ; and other deeper muscles, to which, I pre- 

 sume, the movements of the mouth, as a whole, are due. 

 The muscles moving the gnathites do not, as far as I could 

 make out, extend beneath the basal edge of the mouth. 

 There are, also, powerful muscles giving movement to the 

 basal segments of the pedicel of the first pair of cirri. 

 Again, there are superficial muscles running to the next 

 succeeding thoracic segment ; the anterior ends of which 

 are separated by a clear interspace from the lower ends of the 

 above-described superficial muscles, by which the prosoma 

 is attached to the scuta. On each flank, moreover, but more 

 deeply imbedded, are the long flexor and extensor muscles, 

 presently to be described, running to the five posterior 

 thoracic segments. The last muscle which I need here 



