ZOOLOGY. 



By Theodore Gill. 



GENERAL ZOOLOGY. 



FEATURES OF PROGRESS. 



The progress of Zoology iu the biennial period just past has shown 

 the usual features exhibited during the present deeade. The doctrine 

 of evolution is now not only recognized by all scientific workers in biol- 

 ogy, but it is i)Ostulated as the starting-point for investigations into the 

 affinities of various types, and the eftbrts of biologists are in a great 

 measure directed to the ascertaimuent of the philogeny and derivation 

 of the various types. This has been exemplified during the past two 

 years in attempts at tracing the genealogy of the mamuials, the cephal- 

 opods, and the acalephs, as well as various groups of the branches and 

 classes of the animal kingdom ; as, for example, the caiUiNorous mam- 

 mals, the ungulates, various worms, &c. 



Perhaps the most iiromment feature of the period surveyed has been 

 the discovery of numerous deep-sea types, mostlj^ resulting from the 

 voyage of the English ship Challenger, but in part also the fruits of 

 dredging of minor expeditions and surveys ; for example, the survey 

 of the Caribbean Sea and Gulf of Mexico, under the auspices of the 

 United States Coast Survey ; the explorations of the United States Com- 

 mission of Fish and Fisheries, and the Norwegian expedition to the 

 Arctic Seas in 1S7G to 1878. These several, expeditions and surveys 

 have been fruitful in the finding and revelation of many remarkable 

 forms. So rich have been the results that, as we shall hereafter see, 

 about 2,000 si^ecies of a peculiar group — the Pha^odaria — have been 

 made known by a single naturalist, mostly from the collections of the 

 Challenger expedition. Our knowledge of the fishes of the deep sea 

 has also been greatly increased. 



An especially noteworthy feature in the taxonomy of 1871) and 1880 

 has been the establishment of a number of " orders " in various groups 

 of the animal kingdom. In view of the disparity iu value of these 

 groups, in the several departments of zoology, it seems fitting to utter 

 a few words of caution and explauation in this place. What is an 

 order ? and what shall be the limits to the range of variation of the 

 forms included under such designation '? are <piostions that must nat- 



331 



