476 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Life-histories of Species of Heptagenia.* — "VV. A. Clemens deals » 

 with three new species in this Ephenierid genus and some nymph-stages 

 not previously described. He devotes special attention to the life- 

 histories. The nymphs mostly inhabit swift water, clinging to the sides 

 and under surface of stones. They are adapted to this life by reason of 

 many interesting specializations, chief of which are much-flattened bodies, 

 broad margins to the head, spreading legs with flattened femora, pecti- 

 nated claws, tracheal gills placed dorsally in an overlapping series, and 

 spreading set£e. A few species, however, are qommon in quiet water, 

 notably Heptagenia canadensis, H. frontalis, and B. tripunctata— the last 

 being very abundant. 



The nymphs are active in habit, and when a stone is lifted from the 

 water they scurry over its surface, usually seeking the lower side. In a 

 vessel without anything to cling to they begin clinging to each other 

 and are soon in a single" mass. They feed on alga? on the stones. 



The life-cycle of a Heptagenia is complete in a year. The egg is 

 deposited in the water and hatches in about forty days. The remainder 

 of the mayfly's life is spent in the water as a nymph, with the exception 

 of a short aerial life of from two to four days as a subimago and imago. 

 As the time of emergence approaches, the nymphs probably migrate to 

 the quieter water. The subimago stage lasts about a day. The imagos 

 never appeared in large swarms, as in Ephemera and Hexagenia, but a 

 swarm would consist of perhaps fifty to a hundred individuals. They 

 would begin their flight from three-quarters to half an hour before dusk, 

 dancing up and down in their rhythmic manner at a height of from 

 12 to 20 feet. The females of all the species observed deposited their 

 eggs by skimming the surface of the water and brushing off the eggs as 

 they appeared from the openings of the oviducts. 



Mitotic Spindle in Spermatocytes of Earwig.]"— C. F. U. Meek 

 has inquired into the factors determining the length of the mitotic 

 spindle in the spermatocytes of Forficula auricularia. The length of 

 the spindle at the stage immediately preceding the conclusion of the 

 primary spermatocyte metaphase is not a constant. The length of 

 the spindle at the conclusion of the primary spermatocyte metaphase is 

 not a constant, and is sometimes smaller than that observed at the stage 

 immediately preceding the conclusion. The length of the spindle in 

 the early primary spermatocyte anaphase is not proportional to the 

 amount of chromosome divergence, and is sometimes smaller than the 

 lengths observed at the stages mentioned above. The volumes of 

 the primary spermatocyte cells vary in the metaphase. The length 

 of the spindle at the conclusion of the primary spermatocyte metaphase 

 is not proportional to the volume of the cell. The length of the spindle 

 at the stage immediately preceding the conclusion of the secondary 

 spermatocyte metaphase is not a constant. The length of the spindle 

 at the conclusion of the secondary spermatocyte metaphase is not a 

 constant, and is sometimes smaller than that observed at the stage 



* Suppl. 47th Rep. Dept. Fisheries Ottawa, 1915, Fasc. 2, pp. 131-43 (4 pis. 

 and 1 fig.). 



t Quart. Journ. Micr. Sci., lxi. (1915) pp. 1-14 (2 pis.). 



