45 



the stalk and other parts, is brilliantly orange in colour. Although I think that the evidence 

 of the stains must be relied on, there are two facts which make it difficult to interpret the 

 tissue as muscular in nature. These are (a) the form of the elements of which the tissue is 

 composed, and (A) the mode of connexion of the ti.ssue with adjacent parts. 



With regard to [a] it must be pointed out that the tissue appears to be composed of 

 oval lamellae, and not of typical muscle-fibres. A sagittal section (fig. 140) or a frontal section 

 (figs. 120, 121) will give the impression of muscle-fibres cut longitudinally. It is obvious that if 

 a linear organ appears as a line in sections cut in two planes at right angles to one another, 

 a section in a plane at right angles to both the others will shew it as a point. I have been 

 unable to obtain any sections in which the elements of the problematical tissue appear as a 

 series of points; and, on the contrary, a transverse section (fig. 131) gives the impression that 

 the organ is composed of a series of oval lamellae. These stain in precisely the same way 

 as the typical muscle-fibres of the body, and a certain number of nuclei can usually be made 

 out along their free coelomic borders. This form of the elements of the tissue precludes the 

 possibility that the problematical tissue consists of a mass of solenocytes ; and Mr E. S. Goodrich, 

 who was kind enough to look at one of my preparations, expressed the opinion that the tissue 

 cannot be explained in that way. 



With regard to (<^), it may be noticed that the elements of the tissue are not so obviously 

 provided with an origin and an insertion as would be expected on the hypothesis that they 

 are muscular. This will be seen in such cases as fig. 140 where the lamellae have a free 

 coelomic border, a condition which is also seen in figs. 120, 121, 131. 



If the tissue really consists of dilator fibres, a function which is suggested by the specially 

 wide lumen of the collar-canal seen in fig. 140, it would be expected that the ends of the 

 fibres would originate from the walls of the collar-cavity. In view of the strong development 

 of the tissue in question it is clear that its muscular nature cannot be regarded as proved 

 unless a sufficient origin can be detected. 



In view of these considerations, and of the fact that figs. 47 — 49 seem to shew that 

 the elements of the problematical tissue are connected with the inner wall of the oral side of 

 the operculum, I have endeavoured to find evidence that the origin of the fibres has been torn 

 away from the body- wall, owing to imperfect preservation. Such a view is, on a priori grounds, 

 not improbable, as the elements appear to be very powerful, and might have undergone 

 contraction, during the death of the zooids, sufficient to tear them away from their origin. 

 Fig. 1 3 1 certainly indicates that the coelomic epithelium of the dorsal side of the collar-cavity 

 has been torn away from its basement-membrane; but even in this case, I cannot satisfy myself 

 that the oval lamellae can have originated from that wall of the cavity. The probability that 

 the relations of the tissue, in the preserved material, are not essentially different from those 

 found during life is increased by the considerations (a) that rupture of the connexions of the 

 tissue might be expected to occur, in some cases at least, at the end which is inserted into 

 the delicate dorsal wall of the collar-canal; and no such rupture is observed; {b) that the 

 undoubted muscles of the animal are seldom found to be torn away, at either end, from the 

 basement-membrane to which they are severally related. 



