52 



LUCERNARI.E AND THEIR ALLIES. 



near the broader end, at an acute angle to the longer axis of the oval. A profile 

 {Jhl. 23) of the anchor remhuls one of the spheroidal tip of a tentacle, asymmetrical 

 in outline, and attached obliquely to a shaft which is broader than it is long. 

 Defining the contour of the ovate mass more closely we should say that it is convex 

 on the distal or posterior face, and hollowed by a broad furrow {fig. 24, a*) which 

 trends along its mid-line, on the proximal or anterior f ic- ; it i^, on tlio wliole, com- 

 parable to a date-stone, leaving out the greater proportionate length of the latter, 

 since the ovate mass of the anchor is scarcely more than half again longer than 

 broad. In tlieir usual attitude the anchors are reflexed posteriorly over the juargin 

 of the umbella to a greater or less degree, and sometimes so strongly that from 

 one-half to two-thirds of the ovate mass is hidden from sight when the body is 

 viewed from in front {fig. 22). The anchor proper is altogether an offspring of 

 the anterior parietcs of the umbella, but a part of what appears to form the stem 

 is a projection or ledge {fig. 25, ji^) stretching out from the border (/i) of the 

 posterior parietcs. The line of junction between the ledge and the true stem is 

 clearly marked by the margin of the muscular layer. 



105. The stem of the anchor contains all the elements of the shaft of a tentacle, 

 and these were originally disposed in like manner; but at the present age they are 

 considerably altered, principally in their direction. This applies in particular to 

 the muscular fibres, which are so conspicuous as to demand attention among the 

 general features of these organs, and, indeed, were it not for them the singularly 

 oblique attachment of the stem to the margin of the umbella would readily escape 

 casual observation. They produce the effect of a striation {figs. 23, 25) on the 

 surface in the same way that the ridges of the opsomyoplax appear like striae in 

 the umbella (^ 81). By following these striations in tlieir course from tlie marginal 

 band {fig. 25, to') outwardly it will be noticed tlmt they converge considerably, so 

 as to form a sort of isthmus {in') directly opposite an anchor. Here the striae are 

 parallel for a sliort distance and then diverge as they run out toward the ledge (J') 

 above mentioned (^ 104). The divergence grows stronger as they proceed, and 

 gradually those along the borders of the isthmus pass obliquely around the neck 

 {fig. 23, a') in two opposite directions, following the edge of the ledge, until they 

 meet on the distal side, and then, like those nearer the middle of the isthmus, pass 

 on directly to the ovate mass («'). Between these two extremes there are, of 

 course, all possible grades of obliquity, and consequently the neck or stem appears 

 as if it were twisted, when seen in profile {fig. 23). This portion of the anchor is 

 very short, not more tlian one-half or two-thirds as long as it is broad. It is appa- 

 rently longer, but that is because tlie ledge from the chondrophys sets it out from 

 the umbellar margin, and, moreover, under a moderate magnifying power, it seems 

 to form a part of it. 



106. The ovate mass (a^) is also the homologue of the shaft of a tentacle, but 

 It IS so disguised as to deceive and mislead the observer who is not familiar with 

 its successive stages of development, and very naturally might induce one, in that 

 case, to sec more than a mere resemblance to the spheroidal tip of a tentacle, and 

 set it down as a homologue with the latter. That would indeed be far from correct, 

 as we shall now show by pointing out the remnants of what was once a distinct. 



