L U C E 11 N A 11 1 .E A N 1) T 11 i: I U A L L I E S . 85 



full grown organ, but, although it converges right and Ifft nuu:h nearer to the 

 median line of tlie proximal side than in the last pliase, it does not form a complete 

 circle about the shaft. It is much the thickest on the distal side nearest to the 

 nematocystic knob (oc-), and thins out gradually backwards, and passes insensibly 

 into the ectophragma (/) of the aboral side of the unibella. Its true termination 

 is indicated by tlie disappearance of the coUetocysts, and by tlie edge (/■;') of the 

 muscular layer. It thins out at the same rate at the sides {Jifj. 82), but rapidly 

 loses in depth as it approaches the proximal side, and finally ceases to exhibit its 

 characteristic features, tlie coUetocysts, before it completely embraces the shaft. 

 Its near approximation to the entire encirclement of the shaft is indicated by tlie 

 great thickening of the opsophragma (n^) along the median line of the proximal 

 side. 



170. All of the elements of a complete anchor are here well exemplified, both 

 in point of distinctness and thickness. The opsophragma of the colletocystic 

 portion (oc') is nearly at its full grown maximum thickness on the distal side, near 

 the knob, and equals in this respect the combined depth of the subjacent layers. 

 Curiously enough, though, this proportion is reversed at the base of the organ, for 

 as the opsophragma («") decreases in thickness, the (jaMmpliratjiua (i*) increases in 

 like degree, so as to be nearly as deep as the greatest measurement of the former. 

 At no point, though, is the outer wall as thin as on the umbclla proper; not even 

 where it joins its homologue on the aboral side of the umbella, since there it does- 

 not suddenly cease its diminution in depth, but continues to do so for a short 

 distance backward, until it attains a ccnlain measure, and then spreads Avith a uni- 

 form thickness over tlie aboral area thereabout. The mi/oplax (lu^) is quite thick 

 and sharply defined throughout the anchor, not excepting the tentacular portion. 

 The c1iondyomt/oi>lax (Ir) is also equally well marked with the myoplax, and as 

 thick, on the average, as the gastrophragma, but, unlike tlie latter, is nearly of 

 uniform thickness throughout its length and breadth; only exhibiting a slight 

 thinning at the sides of tlie anchor, and at the base of the nematocystic knob. 

 The <jtiMroj^>hra(jma (?), except along the distal side of the anchor, is generally 

 a little thinner than the cliondromyoplax, but, like tlie latter, tliins a little at tlic 

 sides and at the base of the knob. In accordance with the preponderating 

 weight of the colletocystic mass on the distal side, the internal cavity (oc^) of the 

 latter projects in the same direction, much more than it does in any other, forming 

 on that side a broad diverticulum. The average diameter of the cavity of the 

 anchor in a proximo-distal direction is not more than one-third the measure at right 

 angles to that. Within the base of the globose tip, however, it abruptly thins 

 out to a narrow tube, but at its proximal end it gradually widens (Jig. 82) into the 

 general cavity of the umbella. 



171. The nemafoc/jstigerous, globose tip (oc") of the original tentacular shaft of 

 this organ is quite densely crowded with the larger and smaller kinds of nemato- 

 cysts. Up to this period, at least, there seems to have been an mcr<^ased develop- 

 ment of these cysts, both as regards their numbers and the perfection of their 

 structure. In order that their present condition may be well understood, we refer 

 to the figure (fig. 48) and description of tin; globose tip of a very young tentacle 



