ZOOLOGY. 



By Theodore Gill. 



GENERAL ZOOLOGY. 



FEATURES OF FKOGKESS. 



The progress of Zoology in the bioTinial period just past has sliown 

 the usual features exhibited during the preseut decade. The doctrine 

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

 ogy, but it is postulated as the starting-i)oint for investigations into the 

 aifinities of various tyi)es, and tlie efforts of biologists are in a great 

 measure directed to the ascertainment of the philogeny and derivation 

 of the various types. This has been exeiuplitied during thei)asttwo 

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

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

 classes of the animal kingdom ; as, for exaui])le, the cajni\"orous 7nam- 

 mals, the ungulates, various worms, &c. 



Perhaps the most jirominent feature of the period sur\eyed has been 

 the discovery of luimerous deep-sea typos, mostly resulting from the 

 voyage of the English shi]) 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 Mexi(50, under the auspices of the 

 United States Coast Survej' ; the explorations of the United States Com- 

 mis.sion of Fish and Fisheries, and the Norwegian expedition to the 

 Arctic Seas in 187G to 1878. These several expeditions and surveys 

 have been fruitful in the fiiuling and revelation of many remarlcable 

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

 about 2,000 species of a peculiar group — the Phrcodaria — 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 187'.) 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 dei)artments of zoology, it seems fitting to utter 

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

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

 forms included under such designation ' are (pu'stious that must nat- 



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