6i8 SAMPSON. [Vol. XI. 



of the internal organs, somewhat as in Fig. 3. The oblique 

 dorsal muscles he describes ; the pedal muscles have apparently 

 not been cut away close to their attachments, and Poli there- 

 fore finds a series of "pyramidal muscles." These are evi- 

 dently the internal fibres of the latero-pedal muscles seen from 

 the ventral side, for, by comparing cross-sections with Fig. 3, 

 it will be seen that, if in Fig. 3 the latero-pedal muscles had 

 been cut off only to within some distance from their attach- 

 ment, instead of close to the shell, the fibres of consecutive 

 muscles, as they diverge anteriorly and posteriorly from the 

 shell, would have formed groups pointed toward the median 

 line and spread laterally to meet one another at a level nearer 

 the observer, thus forming pyramids; and there is a pair of 

 pyramidal muscles (the latero-pedal of the anterior and posterior 

 groups) corresponding to each oblique dorsal muscle. Poli 

 describes, outside the pyramids, a circular muscle around the 

 body which is difficult to identify with any one muscle ob- 

 served, but seems rather to correspond to the muscular tissue 

 of the mantle near the shells. The pyramids, he says, go 

 from the circular muscle to the separate shells and bind them 

 firmly; the shells are still more securely bound by "girding 

 muscles " (apparently the muscles of the cushion) and by the 

 serrations at the edges of the shell ; each of these girding 

 muscles, also proceeding from the circular muscle, is attached 

 at its edge to a shell; and the serrations of the shell are deeply 

 imbedded in alveoli, in the circular muscle, as Poli shows in 

 a figure of the dorsal side without the shells. Poli concludes 

 his description of the muscles by showing in a part of the 

 same figure (where the dorsal muscles are cut in the median 

 line and turned back) the " transverse muscles " of the foot 

 that are united together in little bundles. 



Middendorff, writing in 1847, gives a very brief account of 

 some of the muscles of Chiton (Cryptochiton) Stelleri ; he says 

 the muscles in the body-wall (seen on opening the animal on 

 the dorsal side) are continuations of a fiat, muscular sheet, 

 which he calls the " Bauchmuskel " ; this muscle bounds ven- 

 trally the body cavity, and is the innermost layer of the usual 

 organ of locomotion among the Gastropods, that is, the foot. 



