718 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
finds some curious exceptions. Herbaceous plants usually harbour only 
one species of mite, but trees and shrubs almost constantly shelter 
several. The suggestion of Thomas that there were some free-living 
Phytoptidae is confirmed by the strongly developed integuments in the 
species of Phyllocoptes and Acanthonotus, and especially by a species of 
Phyllocoptes (P. schledendali), which Schlechtendal found living freely 
and producing white spots on the leaves of Pyrus malus. 
Acarina from Algeria.* — Mr. A. D. Michael reports on 44 species 
of Acarina obtained during a recent visit to Algeria. A second species 
of the remarkable genus Cseculus was discovered, which was noticeable 
for its size and for the singular arrangement of the hairs on the cephalo- 
thorax. Notaspis burrowdi sp. n. affords an example of the very wide dis- 
tribution of these minute creatures, as it has also been obtained in Canada. 
Damveus phalangoides sp. n. has such very long and slender legs that 
one wonders, when the extreme brittleness of the chitin in this family 
of Acarina is borne in mind, how they can remain unbroken. D. patel- 
loides sp. n. is remarkable for having a pyramidal abdomen. "While 
Nothrus sylvestris has the claws monodactyle, the Italian N. ananniensis 
has them didactyle; a variety of this latter, found in Algeria, is 
tridactyle. 
Ontogeny of Limulus.j — Dr. J. S. Kingsley has a preliminary 
notice of his studies on the development of the King-crab. The result 
of yolk-segmentation is to divide the egg into a number of yolk-cells, in 
the centre of each of which there is a nucleus with a thin layer of proto- 
plasm. As the result of migration a blastoderm is at first formed on 
one side of the egg, the cells of which are smaller and less charged with 
yolk than those of the rest of the ovum. This blastoderm produces a 
lighter spot on one side of the egg which strikingly resembles the 
primitive cumulus of Arachnids. In its centre there appears a small 
circular pit, which is to be regarded as the blastopore. A second cloud 
appears behind the first, and soon surpasses it in size. No endoderm is 
produced by gastrulation. 
In fifteen days the germinal area becomes divided by the appearance 
of a transverse groove into cephalic and postoral plates, and in twelve 
hours more a second groove appears behind the first, and cuts off a 
narrow ridge, which is the first postoral somite. Successive somites are 
added by budding from the caudal until six are formed. Near the outer 
margins of each of these paired thickenings the rudiments of legs arise. 
And, almost simultaneously, paired thickenings for the nervous system 
appear, one in each somite of the body and three in the cephalic plate. 
A few days later a series of six pairs of segmentally arranged sensory 
thickenings arise outside the legs ; these have different fates. The first 
gives rise to the median ocelli of the adult ; the second to a peculiar 
and as yet undescribed sense-organ, which occurs on the thin skin just 
in front of the first pair of appendages ; the third soon disappears ; the 
fourth forms the dorsal organ of Watase ; the fifth gives rise to the 
paired compound eyes, and the sixth pair is evanescent. These organs 
are connected with one another and with the brain by a longitudinal 
* Proc. Zool. Soc. Lond., 1890, pp. 414-25 (2 pis.). 
f Zool. Anzeig., xiii. (1890) pp. 536-9. 
