70 BALANID.E. 



mention, is a deep-seated diverging pair, attached near the 

 upper end of the stomach, on its ventral surface, and di- 

 verging from this point to the sides of the prosoma high up 

 beneath the mouth. The probable action of this pair, as 

 well as of the three superficial pairs of muscles by which 

 the body is attached to the scuta, is to draw up the whole 

 prosoma towards or from the orifice; and likewise to con- 

 I ract it firmly, so as to serve as a fulcrum for the movements 

 of the five posterior thoracic segments, together with the 

 cirri, which they carry. 



The muscles of these five thoracic segments are nume- 

 rous and powerful ; they are also complicated, chiefly owing 

 to the segments on their dorsal and dorso-lateral surfaces 

 being driven, like wedges, one into the other. As far as I 

 could make out, there are on each side three, superficial, 

 dorso-lateral and lateral muscles (generally, if not always, 

 destitute of striae), which do not cross the articulations, but 

 extend merely from articulation to articulation ; and of which 

 the function can be only to contract each separate segment, 

 and consequently to open out the intermediate infolded arti- 

 culations; the effect of this would be to separate slightly the 

 cirri from each other, — more especially those borne on the 

 two or three anterior segments, between which the infolded 

 articulations are deeper or broader. There are other more 

 deeply imbedded, powerful, long, dorso-lateral extensor, 

 and ventri-lateral flexor muscles, attached at one end 

 within the flanks of the prosoma, and at the other end to 

 the successive segments of the thorax. The action of the 

 former is to straighten and stretch out the thorax ; of the 

 latter, or ventri-lateral muscles, to retract it. In tracing 

 these muscles, a fascia could be seen to become attached to 

 a segment, and then this same fascia would run on to the 

 next succeeding segment : the effect of this must be, that 

 each segment can be retracted and protracted either from 

 the prosoma as a fulcrum, or from the antecedent segment 

 as a fulcrum : we have, also, seen that each segment can, 

 by the agency of the superficial, non-striated muscles, 

 contract itself. Hence these thoracic segments are capable 

 of diverse movements, as was very evident when the shell 

 of a living specimen was opened. By one movement in 



