312 Mtscellaneoits. 



from the tube of the parent after it was one third of a line in length, 

 and consisted of ten annuli, including the head, from which pro- 

 jected ten tentacles. — Froc. Acad. Nat. Sc. Philad. Sept. 20, 1870. 



Note on transversely striated Muscular Fibre among tJie Gasteropoda. 

 By W. H. Dall. 



In studying the radula of a species of Acmrea (probably A. 

 horneensis, Eve.) obtained by Prof. A. 8. Bickmore at Amboyna, I 

 noticed, on placing the structure under a power of 100 diameters, 

 that certain of the muscular fibres which adhered to it, when torn 

 from the buccal mass, had a different appearance from the others. 

 On increasing the power to some SOO diameters, it was at once 

 evident that the different aspect of these fasciculi was caused by 

 fine, but clearly defined, trartsverse striation. Suspecting that it 

 was an optical delusion, caused by a very regular arrangement of 

 the nuclei of the fibres, I subjected the muscle to various tests and 

 to still higher magnifying-powers. I also introduced under the 

 same glass some of the voluntary dorsal muscles of a small crusta- 

 cean, for comparison. The structure of the ultimate fibres in both 

 appeared to be similar. These seemed to be composed of a homo- 

 geneous tube or cylindrical band of translucent matter, with nuclei 

 interspersed at irregular inter\-als. In neither was there any ap- 

 pearance 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 fibres, 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 crus- 

 tacean and the striated muscles of the mollusk appeared to be that 

 the latter were much more finely striate, the striae being six to 

 eight times as numerous as in the former, in the same space. Xo 

 difference between the striated and non-striated muscles of the 

 AcmrPM 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 beads, which bore 

 no relation to the position of the true nuclei. The striated fibres 

 appeared, after a careful dissection of the parts in a number of spe- 

 cimens, to be the retractors of the radula ; they were longer and in 

 narrower bands than the non-striated fibres, and comparatively 

 much fewer in number. The striation was most evident toward 

 the middle of the fibres, and became evanescent toward their ex- 

 tremities. 



Lebert and Robin (Miiller's Arch. f. Anat. und 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 miglit, at the first glance, be mistaken for 

 transversely striated muscular fibres. The latter, however, are ac- 

 tually found in one acephalous mollusk, Fecten (and probably in 

 Ldma also), and some annelids," and are constantly present in the 



