MUSEUM OF COMPAKATTVE ZOOLOGY. 163 



SIPHONOPHORA. 



Agalma elegans, Fewkes. 



A. elegans is generally foitnd once or twice each summer in Narragansett 

 Bay. It appears with striking regularity about the end of the month of 

 August. 



In order to illustrate the general form of the adult there is given a life- 

 size figure of one of the largest of these animals which was taken (Plate X.). 

 Figures of the more important members of the colony and of younger stages 

 can be found with explanations on Plate IX. The youngest Agalma figured 

 in the latter plate (Fig. 2) resembles in some respects the genus Athonjbia, 

 and on that accoimt is called the Athorybia stage. It is characterized by em- 

 bryonic covering scales, which have serrated edges, and by peculiar tentacular 

 knobs (Figs. 9, 9"). Nectocalyces are not formed in this stage, and the float 

 is surrounded by a crown of covering scales fastened to an embryonic stem, which 

 is later absorbed. The covering scales of the adult Agalma (Figs. 3, 4) are not 

 serrated along their margins, although their edges are crossed by rows of lasso 

 cells (Figs. 11, 18), the tips of which, when seen in profile, impart the appear- 

 ance of a serration to the border of the scale. The embryonic tentacles of the 

 Athorybia larva never develop into those of the adult. These two structures, 

 or at least the knobs which they bear, are so different in form in larva and 

 adult that there is little doubt that they have different functions (compare 

 Figs. 9, 9% with Figs. 20, 21). 



The embryonic knobs do not resemble the tentacular knobs of the genus 

 Athorybia, but are not unHke those of Nanomia cara, A. Ag. They bear 

 on their distal ends long stiff hairs (cnidofils) which seem to arise from 

 peculiar cells in the substance of the knob. They are non-retractile, and can be 

 made to separate from or approach each other. All together generally when 

 separated at their tips assume a fanlike shape. The mass of the knob itself is 

 made up of large lasso-cells of two kinds. Of these the majority form a pave- 

 ment of cells laid side by side, making a cup-shaped body, which is seen in the 

 upper basal part of Fig. 9. The second kind of cells lie between these and 

 those terminal cells out of which seem to issue the " cnidofils." The em- 

 bryonic knobs have a darker crimson color than that possessed by the adult 

 tentacular pendants. 



The embryonic tentacle of the Athorybia larv'a arises from an embrj'onic 

 polypite (Plate IX. fig. 14,/). This polypite is formed out of the modified yolk 

 sac, and differs from the other polypites, which are formed later by the presence 

 on the side towards the attachment of the tentacle, of a network of bright red 

 pigment spots. The meshes of this latticework of pigment are clearly differ- 

 entiated and well marked. This peculiar pigmentation distinguishes the em- 

 bryonic polypite. All the others, which arise as simple buds from the stem, 

 are destitute of the latticework of pigment found at the base or on the sides of 



