124 On transversely striated muscular fiber in Gasteropoda. 



witli nuclei interspersed at irregular intervals. In neither was 

 there any appearance of separation into transverse disks, as is 

 seen in the striated muscles of vertebrates. That the striated 

 appearance was not due to contraction and folding of the 

 muscle, was evident upon taking a side view of one of the 

 fibers, when the striae on each side, as well as the intervening 

 elevations, were seen to correspond exactly to each other. 



The only perceptible differences between the muscles of the 

 crustacean and the striated muscles of the mollusk, appeared 

 to be that the latter were much more finely striate ; the stris 

 being six to eight times as numerous as in the former, in the 

 same space. No difference between the striated and non- 

 striated muscles of the Acmoea could be observed, except in 

 the fact of the striation. In both the nuclei were irregularly 

 distributed. The appearance of the striated fibre reminded 

 one of a string of rhombic heads, which bore no relation to the 

 position of the true nuclei. The striated fibers appeared, after 

 a careful dissection of the parts in a number of specimens, to 

 be the retractors of the radula ; they were longer and in nar- 

 rower bands than the non-striated fibers and comparatively 

 much fewer in number. The striation was most evident towara 

 the middle of the fibers and became evanescent toward their 



Lebert and Eobin (Miiller's Arch. f. Anat. and Phys., 1846, p. 

 126) state that the primitive muscular fasciculi of invertebrates 

 often have the nuclei and intervening clear spaces " arranged 

 in such regular order that they might, at the first glance, be 

 mistaken for transversely striated muscular fibers. The latter, 

 however, are actually found in one acephalous mollusk, Pectew, 

 (and probably in Lima also), and some annelids," and are con- 

 stantly present in the voluntary muscles of Crustacea and h; 

 secta. In the further researches of M. Lebert (Annales Sci. 

 Nat., t. xiii, 1850, p. 161), he observes that there is nothiiig 

 extraordinary in the discovery of transversely striated muscular 

 fiber in Polyzoa {Eschara) by Milne Edwards, and in J.cfonw 

 by Erdl, since " the further we have pursued the study of the 

 comparative histology of muscular fiber, the more convinced 

 we have become that transversely striated muscular fiber is to be 

 found in a large number of animals of very inferior organiza- 

 tion, without regard to their more or less advanced position m 

 the animal kingdom." 



Striated muscular fiber has lately been shown to exist in the 

 " tail" or appendix of Appendicularia by Moss (Trans, hin- 

 Soc, vol. xxvii, p. 300). It was already known to exist m 

 Salpa, (Eschricht, ov. Salperne), in the articulated brachiopoda, 

 (Hancock, Tr. Roy. Soc, 1857, p. 805), and in Pecten, (Lebert, 

 Annales Sci. Nat 1850, Srd ser., t xiii, p. 166 ; and Wagner, 



