ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
51 
framework ; its corpuscles are derived from such of the mesodermic 
elements as are not used to make the framework. The development of 
Porcellio must he looked upon as condensed. 
Ereshwater Crustacea of Indian Archipelago.* — Prof. M. Weber 
finds that Eutomostraca are incomparably less numerous in Indian than 
in European waters; in discussing the cause of this, he suggests the 
division of the freshwater fauna into — 
1. Universal freshwater animals. 
2. Regional „ „ 
a. Local genuine freshwater animals, which form an already 
ancient stock. 
b. Marine forms. 
a. Relics. 
/3. Immigrants. 
/ 3 r Active immigrants. 
/? 2 . Passive „ 
A list of the species collected by Prof. Weber shows not only the 
relative paucity of Entomostraca, but the fact that all the Isopods 
observed are either exclusively stationary, or permanent parasites, and 
belong either to marine species, genera, or, at least, marine families. The 
Amphipod fauna of Indian fresh waters is totally different from that of 
Europe. While Gammaridae are entirely absent, Orchestiidae are only 
rarely met with, and such as were, were undoubtedly originally immi- 
grants from the sea. 
The list of Decapoda proves clearly the immigration of members of 
this group into the Indian rivers ; some, indeed, have as yet only reached 
brackish water ; what is true then of the Isopod and Amphipod fresh- 
water fauna is true also of the Decapod. 
The Crustacean fauna of the fresh water in the Indian Archipelago 
is composed of (1) forms of universal occurrence, and of (2) regional or 
local animals destitute of the aids to dissemination afforded by smallness 
of body and special gill-arrangements ; they are derived directly or in- 
directly from the sea, and even now fresh elements are continually being 
added to the freshwater fauna, which is of a character quite different from 
that of Europe. 
Stomatogastric System of Astacus and Homarus.| — Mr. E. J. 
Allen gives a detailed account of this part of the nervous system, and 
looking at it as a whole, finds it probable that there are three main 
centres from which motor fibres start and in which sensory fibres end — 
the two commissural ganglia and the gastric ganglion. The two former 
communicate with the central nervous system by means of fibres which 
enter it from the commissures, while they have a special direct com- 
munication with the brain by fibres which pass through the anterior 
median nerve, and bifurcate in the oesophageal ganglion. The gastric 
ganglion is placed in common communication with both commissural 
ganglia by means of elements originating in cells in the oesophageal 
ganglion, the processes of which divide into three main branches. It is 
* Zoolog. Ergebnisse, ii. 2, pp. 528-43 ; translated in Ann. and Mag. Nat. Hist., 
xiv. (1894) pp. 237-53. 
t Quart. Journ. Micr. Sci., xxxvi. (1894) pp. 483-92 (2 pis.). 
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