A COMPARATIVE STUDY OF STRIATED MUSCLE. 43 
in Syllis corruscans, is that of its relationships with the 
tissue of the corresponding organ in other Polycheta. A 
division of the alimentary canal corresponding exactly with 
the “ gizzard” of Syllis is found in a great number of errant 
Annelids. In all, however, of the forms I have examined, 
containing representatives of a considerable variety of families, 
the wall of this muscular part of the pharynx is composed 
entirely of the ordinary non-striated muscular fibres. This 
holds good even of families such as the Hesionidz, which are 
nearly related to the Syllide; and even of a genus, Gnatho- 
syllis, belonging to that family itself. There can be no 
doubt, then, that these two forms of tissue, taking the same 
place in the same organ in nearly related forms, are, directly 
or indirectly, genetically related to one another; and there 
can be just as little doubt, I think, that the striated muscular 
tissue, so exceptional in animals of this class, has been formed 
by modification of the ordinary non-striated fibres. We have, 
then, to look out for some intermediate modifications between 
Tyrrhena or Hesione, in which the wall of the gizzard 
consists of homogeneous doubly refracting non-striated fibres, 
and Syllis corruscans, with its highly developed striated 
fibres. 
Such intermediate modifications are to be found in certain 
species of Polynoé and in various species of the genus 
Syllis. The muscular portion of the pharynx of Polynoé 
corresponds in outward appearance very closely with that of 
Syllis, and this similarity extends to the function and mode 
of action of the organ,! as well as to the outward form. In 
1 The powerful character of the muscular wall of this organ seems at first 
sight in favour of the view that it is of the nature of a gizzard, and that its 
chief function is to crush objects taken in at the mouth as food. But an 
examination of the animals and their movements in the living condition has 
convinced me that, if this is a function of the organ, it is not the principal 
one; the gizzard-like structure is before everything a sucking organ. 
Under certain circumstances the anterior part of the pharynx of Syllis will 
be found protruded ; when fully everted it forms a proboscis, the anterior rim 
of which is surrounded by a circlet of soft flattened papilla, while projecting 
forwards on one side in line with the long axis of the body is the single sharp 
