clx GENERAL SUMMARY OF SCIENTIFIC AND 



Many fish are afflicted by crustaceoiis parasites, called Argiilus, 

 which adhere to the gills. Dr. Clans has recently published an 

 elaborate description of the variable form known as Argulus foliaceus. 

 It is a jDarasite on a great variety of fishes, also on toads and tad- 

 poles, and even on the axolotl or larval salamander. 



The habits and nature of the limbs of trilobites is a matter about 

 which there is much difierence of opinion among naturalists. Some 

 consider that they had broad, leaf-like swimming aj^pendages ; while 

 others think they were like the modern Scrolls, a sowbug-like form; 

 and others compare them to the horseshoe crab, which both burrows 

 and swims, walking through the mud, and at times swimming on its 

 back, by means of its broad, leaf-like, abdominal feet. As a contribu- 

 tion of some value to this subject is a paper by Mr. C. D. Walcott, 

 printed in the Annals of the New York Academy of Sciences, for- 

 merly the Lyceum of Natural History. His observations, based on 

 the examination of 1160 specimens, lead him to believe, with Bur- 

 meister, that they swam on their backs, as out of 1160 specimens 

 1110 lay on their backs. The author seems to agree with the follow- 

 ing conclusions, reached by Burmeister : (1) that these animals moved 

 only by swimming, that they remained close beneath the surface of 

 the water, and that they certainly did not creep about at the bot- 

 tom ; (2) that they swam in an inverted position, the belly upward, 

 the back downward, and that they made use of their power of rolling 

 themselves into a ball as a defense against attacks from above ; and 

 (3) that they most probably did not inhabit the open seas, but the 

 vicinities of coasts, in shallow water, and that they here lived gre- 

 gariously, in vast numbers. 



The reproductive organs of the decapod Crustacea have been stud- 

 ied afresh by M. Brocchi, who concludes that neither the position 

 nor the form of the genital orifices can furnish characters for classi- 

 fying the macrourous forms (lobsters and shrimps), while in the crabs 

 they are, with the external organs, of value for distinguishing fami- 

 lies and species. References are made to M'orks on this subject by 

 the American naturalists Stimpson and Ordway. 



The volume on parasitic animals, by Professor Van Beneden, lately 

 2^ublished, will introduce our readers to the subject of commensalism. 

 A new example is given by Dr. Streets in the American Naturalist^ 

 in the case of a crab found living in the cloacal dilatation of the 

 alimentary canal of a sea-cucumber or holothurian living among the 

 islands of the Pacific Ocean. The crab belongs to the fiimily Por- 

 tunidce, or swimming-crabs, though an aberrant form. It is not only 

 a new species, but, with another species found by Dana at the Fiji 

 Islands, forms the type of a new genus. 



It has been asserted by Bell, contrary to the supposition of Vaughan- 

 Thompson, that the young of the land-crabs, like the lobster and 

 crawfish, have the same form when hatched as their parents. The 



