HATCHING OF GIPSY-MOTH EGGS. 3 



nonliatch points — that is, points at which considerable nonliatch had 

 been noted each year since the start of the " observation-point " inves- 

 tigations. The sixth set, collected as controls, was obtained from a 

 point which had not shown nonliatch. All the clusters thus obtained 

 were kept in a cool place at the laboratory from the time of collec- 

 tion until just before normal hatching time in the spring. Each 

 cluster was then placed in a glass tube and allowed to hatch nor- 

 mally. All larvse thus produced were counted, and later, when 

 hatching had ceased, the remains of the clusters were rubbed over a 

 cheesecloth sifter to separate the unhatched eggs from the hair with 

 which the egg cluster is made. 



As soon as the records from the six sets of collections could be 

 studied it was seen that there appeared to be some connection between 

 nonhatch and cold weather, for clusters obtained from the five points 

 before our normally cold months hatched almost perfectly, while 

 those obtained after the cold season began failed to produce larvae. 



This suggestion opened up a new line for investigation, and ac- 

 cordingly three sets of weather instruments, each consisting of a 

 recording thermometer and a recording hygrometer, were procured 

 and placed in small instrument houses. As the instruments required 

 considerable attention the three houses were placed at points in the 

 towns of Westford, Acton, and Dover, Mass., two being chronic non- 

 hatch and the third no nonhatch, not very many miles from the 

 Melrose Highlands Laboratory. 



The instruments were started September 1, about the end of the 

 laying season, and were run continuously until about May 1, the nor- 

 mal hatching time. They were tested for accuracy at frequent inter- 

 vals to insure true records, a discussion of which will be given later. 



METHOD OF HANDLING ALL EGG CLUSTERS USED IN 

 EXPERIMENTS. 



Egg clusters when brought in to the laboratory were placed 

 where they would be kept cool but not exposed to severe weather. 

 Just before normal hatching time, v\^hich is about May 1 at Melrose 

 Highlands, each cluster was placed in si glass tube large enough to 

 contain it unbroken. This tube was closed with a cotton plug. As 

 soon as hatching was well advanced, the larvse were removed from 

 the tubes and counted. At the end of the hatching season, the re- 

 mains of each cluster were rubbed over a cheesecloth sifter, made 

 by stretching fine-meshed cheesecloth over a frame, to separate the 

 unhatched eggs from the mass of hair with which all clusters are 

 made. These unhatched eggs were then examined microscopically 

 and divided into infertile and nonhatch, the records of each cluster 

 being kept separately. 



MONTHLY COLLECTIONS. 



Some of the clusters collected during the season of 1915-16 proved 

 to be old nonhatch. During the winter, after the new clusters have 

 become weathered, it is difficult to distinguish between old and new. 

 To make certain that only new clusters would be collected, a suffi- 

 cient number of these were marked with lumber crayon at the end of 

 each laying season at the same six points used for the collections 



