86 



LUCERNAKI^ AND THEIR ALLIES. 



beloii'HiK' to the same individual as the anchor. After this time there seems to be 

 a retrograde metamorphosis taking place in the nematocystigerous sphere, corre- 

 sponding to the advancement of the colletocystigerous mass ; but we are pretty 

 well assured that this is rather an arrest of development, and a scattering of the 

 cysts over a wider area, consequent upon the growth and expansion of the walls in 

 which they are imbedded. The decrease in the number of the nematocysts does 

 not necessarily imply a retrograde metamorphosis, for their disappearance may be 

 accounted for in the liabitual falling away of similar bodies in the tentacles, at all 

 ao'es. Such a phenomenon in the tentacles assuredly does not indicate a retro- 

 grade metamorphosis ; and the failure to reappear in the anchors means no more 

 than an arrest of development. In the course of time, therefore, the characteristic 

 feature which enables the observer to identify the tentacles with the anchors dis- 

 appears in the latter, and a totally new one is implanted in its stead. This is but 

 another proof added to the list which sustains us in the belief tliat the so-called 

 retrograde metamorphosis is nothing more than mimetism, and a preponderating 

 development of one or more parts of an organism, subservient to a particular end. 

 (See^f 1'25.) 



172. In the next phase {fi(]s. 26, 27) of the anchor, which we shall illustrate, 

 the colletocystigerous mass (oc") has united across the median line of the proximal 

 face of the shaft (oc^), and thus formed a complete circle about it. The animal 

 bearing this organ measured a trifle more tlian one-fifth, say six twenty-fifths of an 

 inch across the umbella {fiij. 28). The specimen argues a certain amount of 

 irregularity in tlie rate of growth and development of the anchors of this species, 

 as one may judge for himself by comparing the figure of the phase now under con- 

 sideration with that of the one preceding it, when he will observe that, notwith- 

 standing the coUctocystic mass of the older stage is more advanced than that of 

 the younger, the terminal part of the shaft {fig. 83, oc') of the latter is the shorter 

 of the two, and evidently has ceased to grow at an earlier period. The main 

 progress which the oldest phase has made is exhibited by the very heavy pre- 

 ponderance of the colletocystic mass {fijS. 26, 27) on the distal side of the 

 anchor, extending obliquely outward and posteriorly, so as to almost equal the 

 reach of tlie globose, nematocystigerous tip (oc"). The latter, in consequence, 

 arises from the oblique proximal face of the pad, and has rather the appear- 

 ance of a lateral appendage than of a real terminus of the anchor. Still it pre- 

 serves the tentacle-like physiognomy strongly enough to suggest its original form, 

 and the colletocystic mass looks like a huge circular bolster set about its neck. 

 The cavity (oc') of this organ, like the pad, preponderates so strongly on the distal 

 side that at least four-fiftlis of it lies exterior to the longitudinal axis of the original 

 shaft. Therefore, all of the tendencies of development toward a determinate end 

 are here fully marked out, and nothing is Avanted to complete the organ but 

 changes in the proportions of the several parts. 



173. These changes, however, are by no means small, although no new elements 

 are introduced in the process. In the phase just described, the nematocystophore 

 (oc-) arises midway between the two extremes of the colletocystophore (oc') on its 

 oblique proximal face, whereas in the full developed organ {fi,j. 47) the former 



