534 ME. G. C. BOUENE ON THE GENUS LEMNALIA AND 



primitive condition from which the single sulcus of the Alcyouarian, or the sulcus and 

 opposite sulculus of the majority of Zoantharian zooids, may have been derived. In 

 L. rhabdota and L. perhtijla the stomodfeum is not so long as in L. nltida, but it has 

 the same shape and the same arrangement of cilia. 



The Mesenteries. — In all three species of which I cut sections all the eight mesenteries 

 are continued to the lowest ends of the anthosteles. They are therefore continued into 

 the so-called stem-canals, i. e. the anthosteles of the primary zooids. This is also the 

 case in Siphouogoryia, but in some other meml)ers of the ]\ephfhi//'d(P, e. g. Spongodes, 

 only the asulcar (dorsal) mesenteries are continued into the anthosteles of the stem. At 

 a short distance below the stomodseum the mesenteries are reduced to minute folds or 

 ridges, and it is hard to distinguish a mesenterial filament on the sulcar and lateral pairs. 

 But the asulcar pair bears the characteristic ciliated gutter throughout its extent. My 

 specimens were not sufficiently well preserA'ed to admit of detailed study of the mesenterial 

 filaments. The longitudinal muscles on sulcar aspects of the mesenteries are poorly 

 developed, and, as they are not borne ou the longitudinal pleats of the mesogtea, one 

 cannot speak of muscle-banners. In L. rludjdoia, and particularly in L. perisUjla, the 

 longitudinal muscles are better developed at the upper ends of the mesenteries, and form 

 a diagonal Imnd passing from the body-wall to the oral disc. In these species also there 

 is a considerable development of ectodermic musculature at the bases and along the 

 inner sides of the tentacles. Slips of muscle-fibres are also given off to the jiiiinules. 

 These muscles are not nearly so well developed in L. nitida ; and it will be remembered 

 that in the two first-named species the tentacles can be very tightly infolded into the 

 oral disc, whereas in L. nitida thev are only li<?htlv folded over. I could find no traces- 

 of gonads in any of the species which I examined. 



Histology. 



When specimens have lain for many years in spirit, one cannot expect their histo- 

 logical details to be faithfully preserved. My example of L. j-habdotn was badly 

 macerated ; those of L. jjeristyla and L. nitida were better, and I « as able to make out 

 a few points. 



The ectoderm of the oral disc and stomoda^um has already been described, and its 

 structiire is shown in fig. 21., which is a longitudinal section of a very young anthocodise 

 In fully -formed anthocodiye the tentacles and pinnules are covered with a cubical 

 epithelium, continuous witli and generally similar to that of the oral disc. At the bases 

 of the tentacles the superficial ectoderm becomes flatter, and it is reduced to a single 

 flattened layer of cells over the greater part of the anthodete. In some places, however, 

 and especially Avhere new spicules are being lormed and the syndete is being consoli- 

 dated by the thickening of the external walls of the anthosteles, groups and patches of 

 columnar ectoderm-cells are found, and these are proliferating rapidly from their lower 

 extremities. In this manner little nests of rounded cells arc formed, lying on or in the 

 mesogloca. The mesogloea, as is shown in figs. 22, 23, and 24 (PI. 42), is honeycoml)ed with 

 irregular spaces, most of which are occupied by spicules. In decalcified sjoecimens, the 

 organic residue of a spicule may generally be seen occupying the centre of a mesoglceal 

 space {s.sli. in figs. 22 and 24). Some of the spaces, however, especially those near the 



