ZOOLOGY. 427 



larger granular. The numerous oil globules are imbedded 

 just beneath the dorsal integument; but, with the exception 

 of the whitish spot (granular area) in the centre of the disk, 

 is clear and transparent, exhibiting slight iridescence of the 

 convex side. As the name indicates, this organism is Me- 

 dusa-like ; but this likeness becomes still more strikingly 

 manifest when the organism moves. As in Medusae, change 

 of place is effected by the powerful contraction and dilata- 

 tion of the umbrella-shaped body, like the former, forcing the 

 water suddenly from the cup-like cavity. In the energy and 

 rapidity of the contractions, Dr. Hertwig says it is not be- 

 hind any 3Iedusa, provided the little creature is touched with 

 a o-lass rod. Under these circumstances it darts, like a JRho- 

 palonema, through the water as swiftly as an arrow, by the 

 quickly succeeding pulsations or contractions of its umbrella- 

 shaped body. The strongest contractions were produced by 

 osmic acid. The creature, under the action of this reagent, 

 becomes bell-shaped, about half as wide across the free bor- 

 der of the bell as it is high. As in Medusae, the animal has 

 the power of bending portions of the free border of the um- 

 brella inwards; or sometimes the opposite halves of the disk 

 become bent towards each other, like the opposite valves of 

 a mollusk. Altogether, the discovery is a most interesting 

 one, showing, as it does, the wide range of form and physio- 

 logical differentiation which may be exhibited by a very re- 

 stricted group of simple organisms. 



A number of new species of Rhizopods, collected by the 

 Challenger expedition, have been described by II. P. Brady. 



An interesting essay, by V. Sterki, on the In fusoria, espe- 

 cially Oxytricha and its allies, will serve to keep up the inter- 

 est in these organisms. A lengthy paper on the Flagellate 

 Infusoria, by Biitschli, is translated in the Quarterly Jour- 

 nal of Microscopical Science. Flagellate Infusoria, contrary 

 to the dictum of Pasteur, who claimed that neither micro- 

 scopic organisms nor their germs are ever found in the'blood 

 of an animal in health, have been found by T. R. Lewis in 

 the blood of healthy rats. The first volume of the third 

 part of Stein's great work on the Infusoria has appeared. 

 It contains an exhaustive history of the discoveries and 

 writings of previous observers, from Ehrenberg to Carter, 

 Busk, Williamson, Hicks, and James Clark. The author, 



