ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
37 
Mid-gut of Artemia.* — Prof. J. Frenzel describes the lining epithe- 
lium and the process of secretion in Artemia salina , and in an Argentine 
species. Special attention is directed to the hair-fringe of the cells. 
This the author supposes to have a protective function, and suggests 
that it may be saturated with an anti-enzyme. The cells show a 
longitudinal striation which the author interprets as significant of a 
mechanical supporting framework. Towards the hind region of the gut 
the lining cells show minute crystalline needles of a red colour. Frenzel 
believes in two kinds of secretory epithelium, that in which the cells 
persist as permanent glands, and that in which they perish in secreting 
and are regenerated. In Artemia a vesicle forms in the secretory cell, 
the cell increases in size, the hair-fringe is lost, the nucleus disappears, 
and the cell bursts. Sometimes, however, in the anterior part of the 
mid-gut, cells are set free without any vesicle-formation ; they burst into 
fine granules. As to absorption, it is maintained that this may occur in 
Artemia and in other Arthropods, &c., at any part of the food-canal, but 
there is at the same time division of labour, for the fore-part of the mid- 
gut is more secretory, the hind-part more absorptive. 
The author adds a note on the mid-gut cells of caterpillars during 
pupation. The cylinder-cells have more or less red contents (in Sphinx, 
Helias, CEceticus, &c.). Before and during pupation these red cells are 
extruded, as if secretion continued although the gut is empty. 
Early Development of Cirripedia.f— Mr. T. T. Groom publishes an 
abstract of observations made at Naples and Plymouth. The size of the 
ovum has much more relation to that of the nauplius than to that of the 
adult. Fertilization takes place in the mantle-cavity before the cir- 
cumvitelline membrane is formed. After fertilization the egg diminishes 
in size, and commences to undergo rhythmical contractions, which do 
not cease till the protoplasmic and yolk-portions are completely sepa- 
rated ; the former generally collects at the anterior or larger pole, and 
the latter at the posterior or smaller. When the nucleus divides one 
daughter-nucleus remains in the protoplasm, and the other passes into 
the yolk, the elements of which it has the power of transforming into 
protoplasm. The yolk becomes gradually covered by the successive 
emergence of fresh cells, and this process is accompanied by the division 
of the cells cut off from it. The yolk, indeed, may be regarded as 
having the value of a single cell (macromere), which gives off a suc- 
cession of blastomeres (micromeres). The point where the blastoderm 
last covers the yolk nearly always represents the blastopore, and the 
nucleus which gives rise to both endoderm and mesoderm arises at or 
close to the same spot. After separation of the epiblast the yolk-cell or 
macromere still remains as a cell with a single nucleus ; it represents 
both mesoblast and hypoblast ; it immediately divides into two cells 
each of which contains mesoblastic and hypoblastic elements. The 
mesoblast is formed by the cutting off in succession of segments from 
each of the two meso-hypoblast cells, and these form a plug of rapidly 
dividing cells just in front of the closed blastopore. When all the 
mesoblastic cells are cut off the two volk-cells remain as the first two 
hypoblast cells. These last become divided into smaller cells equiva- 
* Zool. Jahrb., v. (1892) pp. 248-70 (1 pi.). 
f Proc. Roy. Soc. Lond., lii. (1892) pp. 158-62. 
