OCR Text |
Show 1888.] MR. G. H. FOWLER ON A NEW PENNATULA. 137 where the two meet. No lateral stripe of siphonozooids is to be found below the lowermost leaves. In transverse section the siphonozooids agree with that figured by Hickson (Phil. Trans, vol. 174, pi. Ii. fig. 10), and exhibit a strong siphonoglyphe (ciliated groove) at the abaxial end of the stomatodaeum. The leaves are placed very obliquely on the rachis, the line of attachment being dorso-ventral. They are approximately triangular in outline, the free sides of the triangle being slightly curved in tbe usual manner. While the lowermost leaves are placed slightly opposite to each other, those in the middle alternate, and the uppermost are again opposite. There are fourteen pairs of leaves in all, in the sole specimen ; of these only the two lowest are rudimentary, that on the left side being less advanced in development than the corresponding one on the right. All the leaves are much contorted, a result probably due to death-struggles. The autozooids (fig. 2) are borue on the uppermost (convex) edge, Transverse section through an immature autozooid. The leaf is bounded above and below by ectoderm, underneath which lies the thick layer of mesogloea (mesoderm), containing spaces filled by spicules previous to decalcification. The stomatodaeum, suspended by the usual eight mesenteries in the coelenteron, is lined internally by invaginated ectoderm, of which the lower (abaxial) three fifths are formed of long columnar cells, bearing stout cilia, and constituting a siphonoglyphe (vide p. 138), X 210. and in a well-grown leaf are 25-29 in number, arranged in three rows, a median and two lateral. In a less mature leaf, such as that figured, they are fewer in number and form 1-2 rows only. They are 4-7 millim. in length, richly charged with the characteristic spicules, and surmounted by eight strong marginal spines, which may be 2 millim. long. Along the dorsal end of the convex border of the leaf they are continued as a row of immature autozooids of varying number, of which the foremost are placed on the rachis, and may even extend to the base of the leaf next above. As has been already stated, thev generally meet at an acute angle with the row of siphonozooids which runs upwards from the ventral surface between tbe leaves. PROC. ZOOL. Soc-1888, No. X. 10 |