ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
353 
the water, and though the males show signs of sexual excitement, there 
is no sort of congress of the sexes. The eggs measure 0 • 2 mm. in dia- 
meter within their chitinous envelope ; they are of a light pea-green 
colour, and the chitinous envelope has a pattern peculiar to each species. 
On the whole, the author’s work confirms that of Kowalevsky, and, as 
he tells us, adds little to it. There may be only one or there may be 
three polar globules, but those in which there was only one were, 
perhaps, not fertilized. When segmentation has resulted in the forma- 
tion of four cells these are not rounded, but elongated in the direction 
of the principal axis. A little later a larger blastoccele appears, which 
is not wholly obliterated during the later development. No twenty-two 
stage was observed, and it is possible that Kowalevsky’s observation was 
made on an abnormal embryo. At four and a half hours gastrulation is 
complete ; the velum shows an hour later, and at eight hours the veliger 
larva emerges from the egg-envelope. 
5. Lamellibranchiata. 
Morphology of Lamellibranchiata.* — Mr. J. H. Kellogg has a pre- 
liminary notice of his studies on Lamellibranchs. He has found muscle- 
fibres with a very distinct cross-striation in the auricle of Ostrea virginiana, 
where the striations are so large that there are but twenty in the space of 
• 03 mm. The secretory epithelium of the byssus, in Cardita borealis, is 
made up of two distinct kinds of cells ; the most numerous are cuboidal, 
and appear to be ciliated. At the inner angles of the deep secreting 
folds there are numerous clear, unstained cells, with faintly striated 
outer ends and indistinct boundaries. The walls of the blood-vessels 
in the byssus organ were lined by an endothelium. 
The nephridium of Pecten has been observed to be a brood- chamber. 
The plate-like gills of Yoldia are able to contract themselves in a variety 
of ways, and very rapidly. These gills have the power of collecting 
food, which is effected with amazing rapidity. The author’s observa- 
tions on the structure of these organs differ considerably from those of 
Mitsukuri ; the rib-like strands which the latter considered to be chi- 
tinous supports are regarded as being muscles, the contractions of which 
effect the movements already mentioned. The thickened edge of the 
gill-plates of Solenomya are remarkable for having the outer cells all 
almost exactly alike ; they are columnar and ciliated, and have a dense 
deeply-staining outer border. The gills of various other forms have been 
examined, and the author states some of the conclusions at which he has 
arrived. The single row of latero-frontal cells, described by Peck in 
Anodon, and the two single rows of Dreissena, were not found in any of 
the marine forms examined, with the exception of Mytilus. Here there 
is an outer single row on either side, and an inner compound row of 
lateral staining cells. The latter arrangement will probably be found 
to be the most usual in Lamellibranch gills. Gland-cells are present at 
the sides — seldom, if ever, in the middle — of the frontal region, and are, 
at times, found in other regions of the filament. The author believes 
that an endothelial lining of the blood-cavity of the filament or plate, 
between the chitinous layers, will be demonstrated in the majority of 
* John Hopkins Univ. Circ., xi. (1892) pp. 80-3. 
2 o 
1892. 
