JJ2 LUCERNAIU^ AND THEIR ALLIES. 



(^ 166-173), these areas are more sharply defined in external appearance, but 

 they do not attain to a well-marked liistological differentiation until a late period. 

 It is true that the colletocysts appear as soon as a change commences on the tenta- 

 culoid shaft, but the corresponding changes in the interior walls are not com- 

 pleted until the animal is probably two-thirds developed in size. 



208. The Edophnujma (Opsopliragma) of the colhtocystophore. In the earliest 

 stages the cells of this layer are identical with those in the shaft of a tentacle, but 

 they soon lose this character, and become gradually, yet rapidly, very deep and 

 prismatic {fi(js. 82, 83, a''), like those in the globose nematocystophore («-), and, 

 at the same time, adherent vesicles (a), the colletocysts, originate and develop in 

 their interspaces. This process goes on until, as described in the previous para- 

 graphs (5[ 160-173) on embryology, the whole shaft is metamorphosed into a thick, 

 pad-like mass of very deep, prismatic cells and imbedded colletocysts. These cells 

 vary considerably in depth in different parts of the full-grown organ {fig. 47, ?j'-), 

 yet they are not subject to changes in length and breadth to any very appreciable 

 extent, since the colletocystophore is relatively far less expansile and contractile 

 than the tentacles. They are most closely allied in form and proportions to those 

 of the globose tip (nematocystophore) of the tentacles, but they arc not so tapering 

 and conoid, since they are arranged in a layer which has a much broader curve, 

 and consequently they approach more closely to a strictly prismatic form. They 

 are conspicuous for their large and dark nucleus-like body {fig. 97, (/'), which 

 is in reality a mass of pigment-granules enveloping a transparent, single nucleus. 

 In this respect they resemble those of the gastrophragma {figs. 94, 95, d}) of this 

 organ, but the nuclear-body is not near as large in the former. 



208 (A). The intercellular colletocysts {figs. 96, 97, a) modify the arrangement of 

 the cells of the ectophragma more ej^tensively than do the nematocysts in the tenta- 

 cles. They lie not strictly in the intercellular spaces, as they are much larger than 

 the cells, but, as it were, on the top of them, in a hollow or deep depression, sunken 

 in the layer. These pits {fig. 96, a') contain from one to three colletocysts (a), 

 and occupy more space than the areas between them. Still this does not appear 

 so, because the ends of the surrounding cells curve inwardly so as to partially cover 

 {fig. 97) the colletocysts, and thus form, collectively, a narrowed entrance to the 

 pit. This arrangement leaves a part of each coUetocyst naked, and ready to adhere 

 to any substance that may come in contact with it. Whether the animal has the 

 power of opening or closing the aperture of the pits, and thus varying the breadth 

 of the adherent surface of the colletocysts, we cannot say ; but if it be so, it must 

 be done indirectly, because there is no contractility in the cells themselves. It is 

 possible, however, that the underlying cells may be forced up by the action of the 

 muscular layer beneath them, and that the colletocysts be protruded through the 

 aperture of the pits. As the colletocysts are colorless, the granular intercellular 

 bodies and the pigmented nucleus of the cells constitute the coloring matter of 

 the layer. Tlie structural details of the colletocysts are to be found in a separate 

 section, or the prehensile organs (§ 30). Occasionally we have also met with 

 nematocysts (Z) intermingled with the colletocysts, but as they are rare, and usually 



