ON THE HISTOLOGY OF THE PEDICELLARLA. 393 
GEGENBAUR in his “Comparative Anatomy ” (French translation by CARL 
Voer, p. 298), remarks concerning Echinoderm muscle :—“ Des recherches 
correspondant aux exigences de la science actuelle sur la structure des 
élements constituant les muscles des Echinodermes nous manquent encore.” 
By treating the muscles of the urchin with different reagents, and making a 
great number of preparations, we have seen all the phenomena which these 
authors describe. Frequently the adductor muscles of the valves of the pedi- 
cellarie are clearly striated, and just as often they do not show the least trace of 
striation. The same is observable in the muscles of the lantern, and we have 
preparations which contain the plain unstriated fibres of WAGNER and FREDERICQ, 
side by side with others where the striation is as distinct as in VALENTIN’s draw- 
ings. More than this, in examining a single fibre throughout its whole length, 
there may often be seen a complete series of gradations between distinct stria- 
tion and the entire absence of striation. The muscles of the spines we have 
also studied, and we have been able to show a marked appearance of striation. 
Mr Haycrart has recently * put forward a new theory on the structure 
of voluntary muscle. He regards the fibrille not as simple cylinders, but as 
presenting wider and narrower portions in succession, so that their striation 
is not caused by an histological differentiation, but is simply an optical pheno- 
menon produced by the unequal refraction which light undergoes in passing 
through the fibril. Without pledging ourselves to a general acceptation of 
this theory, and without asserting that the striation of the muscles of the Echi- 
noderms is due to the same cause as that of the higher animals, we are perfectly 
convinced that the irregularity of the striation in the muscle of Echinus can 
only be explained in this way. The fibres of the lantern show that the dark 
bands correspond with the wide portions of the fibres, and the light bands 
with the narrow portions, and when the edges of the fibre become perfectly 
straight, then the striations disappear altogether (Plate X XI. figs, 14. 15, 16). 
It is probable, as has been already suggested by others, that the striation 
has something to do with the state of contraction of the muscle ; but before 
deciding upon this question, we hope to make further researches, and also 
to investigate the pedicellariz of other Echinoderms. 
This paper was commenced by one of us at the Laboratoire de Zoologie 
Expérimentale at Roscoff in 1878, and continued and concluded by the other 
at the same place in 1880. To M. de Lacaze-Duthiers, as well as to M. Delage 
and the whole staff of the Zoological Station, our most cordial thanks are due 
and tendered. 
* “On the cause of the striation of voluntary muscular tissue,” Proc. Roy. Soc., Feb, 1881. 
