602 SUMMARY OF CURRENT RESEARCHES RELATING TO 



especially algae, attach themselves to snails or mussels, and even to 

 such actively moving forms as Cyclops or Daphnia. Numerous examples 

 of animals are then cited; such as Vorticella, Epistylis, Sponges, 

 Hydroid Polyps, Bryozoa. In some cases (crabs and sponges) a 

 rapacious host hides himself under the cover of his guest. 



Cases of higher symbiosis, in which the guest is not external, 

 are next entered upon, and it is pointed out that, in addition to all 

 these cases in which the host is always passive, there are others in 

 which there is some kind of reaction between guest and host ; thus 

 the crustacean Cryptochirus coralliodytes affects the streams of water 

 which pass to the polyps of its coralline host ; and corals are very 

 frequently indeed affected in form by the Crustacea or mollusca that 

 give in them. In conclusion the author thinks that we gain but little 

 information as to the cause of these symbiotic phenomena, if we are 

 content to say with Van Beneden that there is a " sympathy " between 

 the host and guest. 



Electric Organs of Gymnotus. — G. Fritsch has two appendages to 

 Sachs and du Bois Beymond's great work * on this fish, in which he 

 gives an account of his histological and morphological investigations 

 into the nervous and electric apparatus; he finds support for the 

 doctrine that the electric organs of Gymnotus have been developed 

 from transversely striated muscle, a portion, the lowest lateral 

 muscles, having been separated from the rest to form the so-called 

 intermediate muscular layer, while a superior mass of muscle was 

 converted into the great electric organ. The two are surrounded by 

 a common fascia, which separates them from the so-called small organ 

 which owes its origin to a metamorphosis of the muscles of the fin- 

 rays. No explanation can yet be given of the remarkable variations 

 (within 50 and 100) of the number of electrical columns. Every 

 electric plate of Gymnotus arises from a certain number of primitive 

 muscular bands which become connected together in their middle ; 

 the separate pieces of the compound plates do not, however, seem to 

 correspond to a primitive bundle, but to a primitive cylinder (Cohn- 

 heim) of the embryonic muscle. The mode of termination of the 

 nerves may be most nearly compared with what is seen in the pseudo- 

 electric organ of Baja ; the spongy tissue around the nerve-endings 

 and " thorny papillae " is a supporting substance, directly continuous 

 with the sheath of Schwann. 



In the description of the central nervous system attention is 

 directed to the rounded form, well-developed cell-protoplasm, and 

 broad attachment of the process of the axis-cylinder in the characters 

 of the fully developed electric cell. 



B. INVERTEBRATA. 



Intracellular Digestion.! — E. Metschnikoff directs attention, in 

 this connection, to the hydroid parasite found by Owsjannikoff in the 

 egg of the sterlet ; in the endodermal cells of that parasite were to be 



* ' Unters. am Zitteraal ' (Sachs und du Bois Keymond) 446 pp. (8 pis.) 8vo, 

 Leipzig, 1881. 



f Zool. Anzeig., v. (1882) pp. 310-6. 



