2o8 NATURAL SCIENCE. Sept.. 



different from that of the summer months." The predominant 

 Crustacea also varies with the time of year. 



In Bohemia, at Lake Balaton, which is about thirt3'-six feet 

 deep, " France found that the Plankton animals come by night to the 

 surface, begin to descend at dawn to the deeper regions, remain 

 there until early in the afternoon, when they begin to re-ascend, 

 suddenly appear at the surface shortly after sunset, and there remain 

 overnight." " His view is that the animals seek the cooler waters." 

 But at Lake Mendota "there is practically no diurnal movement of 

 the Crustacea, or, if any, it is downward by night and upward by day," 

 and Dr. Otto Zacharias is quoted as announcing, from observations 

 made in the middle of September at Plon in Holstein, that the 

 plankton of that lake shows no diurnal movement. 



Other statements may be adduced which show that the subject 

 is not a little complicated. Thus, de Guerne and Richard, writing in 

 1889 on the freshwater Calanidae, say, " it is certain that various 

 types, Diaptomus graciloides, for example, are met with at the surface 

 as well by day as by night ; others, such as Hetevocope saliens, have 

 been found much more abundant by night than by day ; but these 

 are only isolated cases, to be explained, perhaps, by special circum- 

 stances (the search for food, etc.)." They note that Limnocalanus 

 macvuvus lives generally in the cold waters of the bottom of the great 

 lakes, yet that specimens have been taken out in the daytime at the 

 surface in the Gulf of Bothnia, Giesbrecht finds that in the Gulf of 

 Naples the Copepoda are abundant at the surface in winter and 

 scarce in summer, most of them at the latter season descending into 

 deep water, though a few species swarm at the top. He is inclined 

 to suppose that the diurnal migrations of pelagic animals take place 

 under the influence of light, the annual under the influence of 

 temperature. 



To the report on Lake Mendota, ample as it is, some additions 

 would still be of advantage. The temperature of the water in July is 

 given only for the surface, and not for the lower levels. The 

 ingenious dredge employed could only be used vertically. It is 

 probable, therefore, that the actual floor of the lake was not explored, 

 as that could scarcely be effected except by horizontal dredging. 

 The observers do not appear to have noted whether the specimens, 

 from whatever level they came, were, as a rule, captured alive. 

 Nothing is said of the enemies to which the various Crustacea are 

 exposed at each or every season in this particular lake. In various 

 waters the conditions of safety, comfort, and food-supply must be 

 so diversely combined for the several species that the habits of many 

 are likely to vary more or less according to the place of abode, as 

 well as according to the time of year. For determining such 

 questions numerous observations are needed, and it must be allowed 

 that Professor Birge and his friends have made a highly useful contri- 

 bution towards the required series. T. R. R. Stebbing. 



British Moths. 



The Lepidoptera of the British Islands. By Charles G. Barrett, F.E.S. 

 Vol. ii. (4 parts). Heterocera, Sphinges, Bombyces. 8vo. Pp. 372. London : 

 L. Reeve & Co , 1895. Large paper edition with coloured plates (41-86). Price 

 each part, 3s. plain, 5s. coloured. 



Just two years have passed since the first volume of Mr. Barrett's 



work, dealing with the British butterflies, was noticed in our pages. 



The present volume contains the first instalment of the moths. A 



