February 3, 1893.] 



SCIENCE. 



59 



particularly adapted for its occupancy. But, no sooner is this 

 done than the individuals along the frontier begin to adapt them- 

 selves to an environment but slightly unfavorable, and, as their 

 adaptation changes, so do they slovk'ly advance outward from the 

 territory originally occupied. A series of unfavorable seasons 

 might occasion the occupation of a wide margin of adjoining 

 country, while a series of unfavorable seasons might sweep this 

 tide of advance back to the place of its origin. But, as the re- 

 ceding tide of the ocean leaves many pools of water in the de- 

 pressions of rock, so will there be left, in especially favorable 

 nooks, a few of the insects which will retain their hold and form 

 small, local colonies, of perhaps not more than a few individuals, 

 and the offspring of these will meet the invesligator long dis- 

 tances from the real habitat of the species. There is scarcely a 

 collector who does not know of one or taore small, secluded 

 areas, in his neighborhood, that are rich in varieties, and which 

 he seldom visits without satisfaction, and frequently he is aston- 

 ished at his success. How long this ebb and flow has been going 

 on, and how many species have been brought to us in this way, 

 are problems we are yet unable to solve. Therefore these facts 

 have been brought together, and are here presented, not as a 

 finished, nor, indeed, as an advanced study, but rather as a pri- 

 mary outline, to be revised and modified as our knowledge of the 

 geographical distribution of our species shall be enlarged by 

 additional study and research. 



A SKELETON OF STELLER'S SEA-COW. 



BT BARTON W. BVEBMANN, PH.D., ASSISTANT, DIVISION OF SCIEN- 

 TIFIC INQUIRY, U. S. FISH COMMISSION. 



DtJEiNG the time from March to September of last year the 

 U. S. Fish Commission steamer " Albatross" was engaged, under 

 the direction of the State and Treasury Departments, in making 

 investigations regarding the habits, distribution, and abundance 

 of the fur seal in Bering Sea and the North Pacific Ocean ; and 

 it was my good fortune to accompany the vessel as senior natu- 

 ralist. 



While carrying on these investigations, we had occasion to 

 visit the Commander Islands, situated in Bering Sea, off the 

 coast of Kamchatka about 80 miles. We spent the first week of 

 June on or about these islands, and in this article I wish to call 

 attention to one of the most interesting and valuable results of 

 our visit to Bering Island, the more important one of the group. 

 This was no less than the discovery of a nearly perfect skeleton of 

 the now extinct Steller's sea-cow, Bytiiia gigas. 



This remarkable animal was first discovered in the fall of 1741 

 by Captain Vitus Bering when his ship was wrecked upon the 

 island now bearing his name. Geo. W. Steller was the surgeon 

 and naturalist of Bering's party, and it is to him that we owe 

 about all that we know about the sea cow in life. 



At the time of its discovery this lai-ge marine mammal was 

 quite abundant about Bering Island, as Steller reports that he saw 

 them in great herds feeding upon the kelp and other sea- weeds that 

 grow in abundance in the shallow water about the island. It was 

 soon discovered that the flesh of the sea-cow was good eating, and 

 the men killed many of them for food. 



According to Steller, the sea-cow when fully grown was 24 to 

 30 feet in length, 20 feet in girth, and weighed 6,000 to 8,000 

 pounds. It was of a nut-brown color and covered with hair, 

 matted like the outer bark of a tree. The skin was exceedingly 

 thick, and so tough that the hunters had to cut it with an ax. 

 The head was very small when compared with the great size of 

 the body, the jaws were toothless, but were furnished with a 

 thick, hoi'ny pad. The anterior limbs were modified into flippers, 

 while the hind limbs were entirely absent, and the tail was widely 

 forked, as in the sperm whale. 



This animal was gregarious, stupid, sluggish, and comparatively 

 helpless, being imable to protect itself by diving, and was occa- 

 sionally washed ashore by breakers. 



When, in 1743, the news of the discovery of Bering Island 

 reached Kamchatka, several expeditions were fitted out for the 

 purpose of hunting the sea-cow and the various fur-bearing ani- 

 mals, such as the sea- otter, fur seal, and blue fox, which are 



found there; and very soon many whaling vessels began to stop 

 there to lay in a supply of sea-cow meat tor food. So great was 

 the destruction wrought by these whalers and fur-hunters that 

 by 1754, only 13 years after its discovery, the sea cow had become 

 practically exterminated. In 1768, according to the investiga- 

 tions of Dr. L. Stejneger of the National Museum, who has made 

 a most careful study of the question, this large and important 

 marine mammal became wholly extinct, the last individual ever 

 seen alive having been killed in that year; and the fate which 

 overtook Eytina so speedily has almost become that of the buffalo, 

 and will as certainly become that of the fur seal unless it be pro- 

 tected. 



Mr. Frederic A. Lucas of the National Museum has recently 

 published a most interesting and valuable paper on "Animals 

 Recently Extinct or Threatened with Extermination," in which 

 he gives in readable form about all that is known of the sea-cow. 

 In this paper, of which I have made free use in the present arti- 

 cle, Mr. Lucas states that, up to 1883, but two skeletons of the 

 sea-cow were known. One of these is in the Imperial Museum 

 at St. Petersburg, and the other is in the Imperial Academy of 

 Helsingfors. There are two ribs in the British Museum. During 

 Dr. Stejneger's stay of about two years (1882-1883) upon Bering 

 Island, he succeeded in finding a number of skulls, ribs, vertebrae, 

 and other bones. One complete skeleton was found buried in 

 the sand, but the bones were too far decayed to permit handling. 

 From the various individual bones found by Dr. Stejneger a 

 fairly good skeleton was "made up," which is now in the National 

 Museum. This, together with the two skeletons at St. Petersburg 

 and Helsingfors, and the two ribs in the British Museum, con- 

 stituted the total amount of material pertaining to Rytina found 

 in the museums of the world at the time of my visit to Bering 

 Island. 



Being conversant with these facts, imagine my surprise and 

 delight upon learning, soon after landing, that a native had re- 

 cently found a nearly perfect skeleton in a good state of preserva- 

 tion, and that he would sell it. I took the first opportunity to 

 examine the skeleton, and was not slow in deciding that it should 

 be purchased for our National Museum. This skeleton was found 

 in 1891 by the same native who found the one which was sent to 

 the Czar. It was embedded in the sand to a depth of a few 

 inches, and lay several rods from the present water-line. It is in 

 a good state of preservation and proves to be very nearly com- 

 plete. The cervical vertebrae are complete and show that the 

 number is seven instead of six a point that was in dispute until 

 settled by the study of this skeleton made by Mr. Lucas of the 

 National Museum. 



Unfortunately the anterior limbs are incomplete, and whether 

 Steller's sea-cow had any hand or finger bones must still remain 

 an unsettled question. 



PLANT DISEASES, CAUSED BY NEMATOID WORMS OF 

 THE GENUS APHELENCHUS BAST. L 



BY I?R. J. RITZEMA BOS, MEMBER OF THE INTERNATIONAL PHYTOPATHO- 

 LOGICAL COMMISSION, PROFESSOR OF ZOOLOGY AND ANIMAL 

 PHYSIOLOGY, AGRICULTURAL COLLEGE, WAGENINGEN, NETHER- 

 LANDS. 



Bis vor kurzer Zeit waren bios aus den Nematoden Gattungen 

 Heterodera Oruff nnd TylenchusBastianinF&auzenschmarotzende 

 Arten bekannt ; in den letzten drei Jahren gelang es mir drei neue, 

 bisher unbeschriebene Species aus der Gattung Aphelenchus Bas- 

 tion als die Ursache von Pflanzenkrankheiten zu entdecken. 



Bekanntlich sind die Aphelenchen den Tylenchen nachst-ver- 

 wandt; es sind beide aalformige Anquilluliden mit schwach 

 geringelter Cuticula und mit einem Mundstachel hinter der 

 Mundoffnung zura Durchbohren von Zellwanden. Wahrend 

 aber bei Tylenchiis der Darm in der halben Lange des Oesophagus 

 eine kugelformige oder ovale muskulose Auschwellung (den 

 " Muskelmagen ") besitzt, und nachher am Hinterende des Oeso- 

 phagus eine nochmalige Auschwellung (den "Magen"), findet 

 sich bei Aphelenchus wohl das erst genannte, nicht das zweite 

 Organ, sodass der eigentliche Darm unmittelbar hinter den Mus- 

 kelmagen anfangt. Es haben weiter die Milnnchen der Tylenchus- 



