238 THE ZOOLOGIST. 



EDITORIAL GLEANINGS. 



Prof. M'Intosh continues, in the last number of the ' Annals and 

 Magazine of Natural History,' his " Notes from the Gatty Marine 

 Laboratory, St. Andrews." In this instalment we meet with a note 

 " On the Frequency of the Occurrence of Pearls in the Mussel (Mytilus 

 edulis)," &c. The frequency of the occurrence of pearls in the various 

 marine and fresh-water shells is fixed by no law. Hundreds of pearl- 

 shells may be examined without finding a single pearl, but, on the 

 other hand, a single Ceylonese shell will occasionally produce a pearl 

 worth a large sum. An experienced pearl-fisherman of the Tay con- 

 sidered that perhaps one in a hundred contained a marketable pearl. 

 From an examination of seven hundred Mussels in the estuary of the 

 Eden, undertaken by Mr. Russell, there was a proportion of 42*8 per 

 cent, of pearl-bearing Mussels. In conclusion, the writer remarks that, 

 " in connection with Dr. Lyster Jameson's views that the Eider-duck 

 and the Scoter are the final hosts of the parasites which form the 

 nuclei of the pearls, it may be stated that both occur in considerable 

 numbers in the estuary of the Eden, and feed on the Mussels. More- 

 over, the intestine of the Common Scoter in St. Andrew's Bay harbours 

 large numbers of these and other parasites, and thus is in contrast with 

 that of such forms as the Guillemot and Red-throated Diver — birds 

 more purely piscivorous, and in which such parasites are rare, though 

 cestodes are common. It is possible also that other species amongst 

 the many birds frequenting the Mussel-beds, such as the Oyster- 

 catcher, may be found to harbour the same parasite." 



In the June issue of the ' Irish Naturalist ' will be found a most 

 suggestive paper by Mr. C. B. Moffat (originally read before the Dublin 

 Naturalists' Field Club) on " The Spring Rivalry of Birds." The writer 

 approaches the question, " Why birds — and perhaps the higher vertebrate 

 animals generally — do not increase in number from year to year." He 

 does not altogether accept the Darwinian explanation of the "struggle 

 for existence," nor does he the theory of " sexual selection." In fact, 

 as regards birds, he assumes that each male bird is " cock of his walk," 

 that he maintains his ground by combat, and that thus a very large 



