BIOLOGY OF PARACOPIDOSOMOPSIS. 39 



developed into a brood of males. A summary of the experiment 



is as follows: 



Host eggs laid the night of November 7. 



Each egg parasitized by one oviposition of an unfertilized female, 



2:30 P.M., Nov. 8. 

 Caterpillars hatched Nov. 13. 

 First brood of parasites preserved Dec. 4. 

 Second brood of parasites preserved Dec. 5. 

 Carcass of third caterpillar formed Dec. 6. 

 Series of pupa stages from carcass preserved Dec. 7 -I 9- 

 Brood of 1842 male parasites emerged Dec. 25. 



We have used a great variety of fixing fluids on polyembryonic 

 material, but for the cytology of male germ cells no reagent has 

 been found that equals Bouin's picro-formol-acetic mixture to 

 which crystals of urea have been added. Preparations of the 

 gonads fixed in this fluid and treated with Heidenhain's iron 

 hsematoxylin, counterstained with Orange G, give very fine 

 results. However, this method of fixation has the disadvantage 

 of not being adapted to the staining technique usually employed 

 to bring out certain cytoplasmic structures, such as the mito- 

 chondria. Nevertheless, we have used it almost exclusively 

 because of our especial interest in the chromosomes. 



Even with the use of the best methods of technique, Hymen- 

 optera material is never as favorable for the study of chromo- 

 somes as that of many other insects, notably the Hemiptera 

 and Orthoptera. In certain respects, the germ cells of Para- 

 copidosomopsis are more favorable for cytological study than 

 those of many other species of the order, but even in this species 

 the chromosomes are, at certain stages, greatly elongated, with 

 a consequent tendency to become entangled with one another. 

 This often makes difficult the determination of the exact number. 

 The difficulty is somewhat increased by the smallness of the 

 cell, which at the end of the growth period does not exceed a 

 diameter of seven or eight microns. The best counts of chromo- 

 some numbers are obtained in somatic cells, because in these 

 cells the metaphase plate is flat and the chromosomes are more 

 scattered than in the spermatocytes. In any event, one does 

 not experience difficulty in distinguishing a metaphase plate 



