ZOOLOGY AND BOTANY, MICROSCOPY, ETC* 
597 
5. Arachnida. 
Embryology of Euscorpius italicus.* — Mr. M. Laurie has investi- 
gated the development of the Scorpion, on which no detailed work has 
been done for twenty years. It is exceptional among Arthropods in 
that the whole development takes place within the ovarian tubes, and the 
history does not agree with any other Arachnid type as yet described. 
The development of the eye has been accurately worked out by Parker, 
but the author has been able to add deta.ls as to the earlier stages and 
as to the connection of the eyes with the cerebral invagination. The 
author’s observations confirm the conclusions of Lankester and Bourne, 
but afford no support to the views of Patten. 
The mode of formation of the ventral nervous system is exceptional 
among Invertebrates, and resembles rather that of the Chordata, for the 
nerve-chord, instead of peeling off from the superficial layer of epiblast, 
sinks down bodily, and is covered by a layer of epiblast which grows over 
it from each side. From the history of its development there can be little 
doubt that the coxal gland is a nepliridium, and it seems probable that 
the genital tubes are, in part at least, nephridial. The gill-books are 
undoubtedly comparable to the abdominal appendages of Limulus, but 
their mode of origin is still open to some doubt. The author thinks it 
quite conceivable that there have been changes in the conditions of 
development, due to terrestrial life and the consequent pressure on the 
embryo. 
The mesoblast consists at first of a pair of segmented bands with a 
separate coelomic space in each somite and also one in the cephalic 
segment. The coelomic spaces soon unite, and the mesoblast bands 
join across the ventral surface. Later on, they extend round — the coelomic 
space extending with them — and unite in the middle line on the dorsal 
surface, where a thickened band gives rise to the heart. A portion of 
the coelom in the seventh segment becomes separated off to form the 
genital tubes. The outer layer of the mesoblast forms chiefly the 
muscles of the body, while the inner layer becomes folded so as to 
surround the liver and intestine, and the coelomic space becomes partly 
filled up by trabecular tissue. 
American Spiders.t — Dr. Henry M‘Cook has nowhere shown the 
thoroughness and enthusiasm of his study of animals more happily than 
in this valuable work. The first volume of the book is all that is at 
present published ; and, considering the scheme of the whole work, we 
should have preferred to see the last or third volume first ; that volume 
will treat systematically of the spider fauna, especially the Orb-weavers 
of the United States. The European reader is unable to follow as intel- 
ligibly and with as much interest as he otherwise would, for want of cer- 
tainty about the specific character and geographical distribution of several 
of the forms, concerning which most interesting details are furnished. 
That which distinguishes Dr. M‘ Cook’s work is the completeness 
* Quart. Jouru. Micr. Sei., xxxi. (1890) pp. 105 -41 (6 pis.). 
t ‘American Spiders and their Spinning Work. A Natural History of the 
Orb-weaving Spiders of the United States, with special regard to their industry and 
habits.’ By Henry 0. M‘Cook. i., Philadelphia, 1889, sm. 4to, 369 pp., 354 figs, 
in text. 
1890. 2 U 
