ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
57 
Anatomy of Bdella arenaria.* — Dr. L. Karpelles gives a detailed 
account of the anatomy of this Mite, which has a body from 0 • 6-0 * 7 mm. 
long, 0-2-0 *3 mm. broad. The endoskeleton is more strongly deve- 
loped than in any Mite known by the author. The stigmata of the 
trachea lie at the base of the mandibles. There are three pairs of 
dilatator muscles to the oesophagus. The central venous system is of 
considerable length; tactile setae are not well developed. An organ 
surrounding the mouth is compared with the preventricular gland of the 
Oribatidae lately described by Mr. Michael, but the author was unable 
to find its efferent duct. The concretions in the excretory organ appear 
to consist of oxalate of calcium or salts of uric acid. The female organs 
consist of an ovary, two oviducts, the uterus, vagina, and an accessory 
gland. 
e. Crustacea. 
Myology of Palinurus Edwardsi.j — Prof. T. Jeffery Parker and 
Miss Josephine G. Rich find, contrary to the teaching of all the text- 
books, that the great ventral mass of muscle in the abdomen is not 
exclusively a flexor, but gives rise to slips which, being inserted into 
the terga and pulling in an almost horizontal direction, must act as 
extensors. The ventral muscles are far more complex than is ordinarily 
supposed, and the authors have had to make several new terms. The 
muscle called levator abdominis is found to rotate the abdomen on the 
cephalothorax. Several bands pass between the telson and the lateral 
tail-lobes, and so serve to approximate the parts of the fin during exten- 
sion of the abdomen. The mandible is acted on by three adductors and 
two abductors. 
Germinal Area of Mysis.J — Prof. R. S. Bergh has set himself the 
task of determining the structural relations between the germinal areas 
of Annelids and Arthropods, and has begun with Mysis. His investi- 
gations begin at the stage when the blastoderm has spread over the yolk, 
forming a simple layer of large, flat cells, and when there are as yet no 
nuclei or yolk-cells. At a definite zone the blastoderm soon thickens, 
forming a transverse band, lying in a shallow depression. This ger- 
minal disc is at first single-layered, but by proliferation in its median 
region a deeper inner layer is rapidly formed. In the superficial layer 
an arch of sixteen large cells becomes clearly defined — the “ Urzellen ” 
of the ectodermic part of the germinal area ; and the deeper inner cells 
are differentiated into (1) yolk (vitellopliagous) cells which migrate into 
the yolk, (2) a compact endoderm-plate from which the epithelium of 
the mid-gut and liver arises, and (3) eight myoblasts or “ Urzellen ” of 
the mesoderm. 
Subsequently the ectoderm becomes differentiated into what may be 
called a nauplial and a metanauplial rudiment. The first consists of 
polygonal cells which show no regular arrangement in longitudinal and 
transverse rows, and are derived from ordinary blastoderm cells ; the 
latter consists of regular longitudinal and transverse rows of cells which 
arise from the “ Urzellen ” proper. From the first rudiment arises the 
* Abb. Zool. Bot. Ges Wien, xliii. (1893) pp. 421-30 (2 pis.), 
t Macleay Memorial Volume, Sydney, 1893, pp. 159-78 (5 pis.), 
j Zool. Jahrb. (Abtb. Auat.), vi. (1893) pp. 491-528 (4 pis.). 
