VIEGULARIA MIRABILIS. G5 



We have not noticed any perforations in the walls separating the 

 several polypes of a leaf from one another, such as are described and 

 figured by Kiilliker as occurring in Halisceptrum and other genera. 



The body-walls of Virgulnria, as already noticed, contain no 

 spicules ; differing in this respect most markedly from those of 

 Pennatuh 



b. The Calij.r. — This forms (Fig. 5, g), a wall surrounding the 

 tentacles when these are either partially or wholly retracted. It 

 differs from the calyx both of FiniiotUna and Pennntula in several 

 respects. It has no strengthening spicules, and it is not produced at 

 its margin into pointed processes, alternating with the tentacles, as 

 is the case in the other two genera. The most important point of 

 difference, however, lies in the fact that while in FunicuUna and 

 Pennatula the calyx is a permanent fold of the body-wall, in Virgularia 

 it is only a temporary one and disappears altogether when the tentacles 

 are fully expanded. This will become clear at once from an 

 examination of Fig. 5, in which the several polypes of the leaf are 

 drawn in different stages of expansion or contraction. Thus the 

 second and seventh polypes, numbering them in order from the dorsal 

 to the ventral surface, are shown almost completely retracted, and in 

 these the calyx forms a deep fold of the body- wall surrounding the 

 whole length of the tentacles. In the third and fifth polypes the 

 tentacles have commenced to protrude, and it will be seen that as they 

 rise up the calyx wall unfolds with them. In the sixth polype the 

 tentacles are almost fully expanded, and the calyx is now reduced to a 

 very low wall surrounding their bases. The fourth polype is drawn in 

 a fully expanded condition, and it will be seen that the calyx (Fig. 5,^), 

 is completely unfolded, and has in fact ceased to exist ; its position 

 being indicated only by a slight wrinkling of the body-wall at the base 

 of the tentacles, and even this disappearing in extreme protrusion of 

 the tentacles. 



If this figure be compared with those already given of FunicuUna 

 (Plate II., Fig. 10) and Pennatula (Plate III., Fig. 4), it will be seen 

 that the calyx is formed in exactly the same way in all three cases, by 

 an infolding or inversion of the upper end of the body-wall ; and that 

 the difference, which is clearly connected with the existence or non- 

 existence of spicules in the calyx, lies in the fact that in Virgularia 

 this calyx-fold is completely everted and straightened out when the 

 tentacles are fully expanded, while in the other two genera it is only 

 partially so, the fold being to a certain extent permanent, the calyx 

 still persisting even when the tentacles are protruded to their utmost 

 extent. 



c. The Tentacles (Fig. 5) are very similar to those of the other two 

 genera. They form a whorl of eight hollow processes arranged round 

 the mouth, each bearing along its inner edge a double row of pinnules. 

 Each tentacle consists of an outer layer of ectoderm cells continuous 

 with those of the body-wall, a middle layer of mesoderm cells, con- 

 sisting chiefly of muscular fibres arranged in an outer longitudinal and 



