ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
605 
Structure of Xenia.* — Dr. J. H. Ashworth gives a full description 
of an Alcyonaceous coral, Xenia hiclcsoni sp. n., from North Celebes. 
The exceptionally perfect preservation of the specimens made a study 
of the minute internal structure possible. The species appears to differ 
from most if not all other members of the genus in the absence of 
spicules from the tentacles and pinnules. 
Among the new points particularly noted are the following. The 
ventral and lateral mesenterial filaments usually present in the polyps 
of Alcyonaria are absent. Their absence is correlated with the presence 
of gland-cells in the stomodseum, especially in the ventro-lateral walls 
which abut on the siphonoglyph. The non-retractile nature of the 
bodies of the polyps and of the stems is accounted for by the absence 
of muscle-fibres from their ectoderm cells and by the presence of 
numerous spicules. But there are ectodermic muscles in the tentacles, 
pinnules, aud distal millimetre of the bodies of the polyps; and as 
spicules are absent from these parts, there is slight contractility. 
An extraordinary number of spicules is present in the basal part of 
the colony, and much of the mesogloea is converted into a dense horny 
substance. Thus a firm base is formed. Many of the endoderm cells 
lining the coelentera and tentacles bear giant flagella. 
In adult polyps the primitive genital cells are formed by differentia- 
tion of some of the endoderm cells which cover the mesenteries. These 
genital cells migrate into the mesogloea of the mesenteries, and then 
move outwards, one at a time, each cell pushing the endoderm and a 
thin film of mesogloea before it, and so forming a small tubercle on 
the side or end of the mesentery. By division of the genital cell the 
spermatozoa are formed, and they remain until ripe, surrounded by a 
thin film of mesogloea and by a layer of endoderm cells. 
The longitudinal canals traversing the mesogloea of the stem are 
very well developed, and are physiologically, and possibly morpho- 
logically, equivalent to the coenenchymal tubes of Heliopora coerulea. 
The nervous system resembles that of Alcyonium ; the stellate cells 
immediately outside the endodermic muscle-fibres are very clearly seen. 
Dr. Ashworth describes a complete series of developing polyps both 
in Xenia hiclcsoni and in Heteroxenia elizabethse, the dimorphism of the 
latter being confirmed. 
He traces the origin of the buds of Xenia hiclcsoni from the super- 
ficial canal system, their subsequent growth and differentiation. It is 
remarkable that the sex-cells are already differentiated in a young polyp 
0*95 mm. in length. 
Porifera. 
Structure of Larva of Spongilla lacustris/f — Mr. R. Evans has 
investigated this subject in regard to which contributions and con- 
tradictions have abounded. His chief conclusions are the following. 
There are different types of free-swimming larva, which are de- 
scribed as A, B, C, and D. Type A is the youngest form of all ; type 
B is an intermediate form between A and C ; while type D is a variation 
derived along a different line of development from type A. 
* Quart. Journ. Micr. Sci , xlii. (1899) pp. 245-301 (5’pls.). 
t Tom. cit., pp. 363-176 (7 pis.). 
2 s 
1899 
