THE DETERMINATION OF SEX 



student of the sexual cells of a grasshopper such as all our 

 students are given opportunity to see. In every nucleus one 

 finds a single round, dark body, the ac- 

 cessory chromosome. The remaining 

 chromosomes are all drawn out and have 

 irregular outlines, so that the accessory 

 chromosome is conspicuous. 



Our next pictures, Figs. 36-40, are 

 taken from Anasa tristis, and are after 

 drawings by Miss Pinney. Anasa tristis 

 is a species of Hemiptera very common 

 with us. The spermatogenesis of this 

 insect has been investigated by many 

 Americans: by F. C. Paulmier 1899, by E. 

 B. Wilson 1905 and 1907, by Miss Foote 

 and Miss Strobell 1907, by Professor 

 Lefevre and Miss McGill 1908, by C. V. 

 Morril 1901, and by Professor McClung 

 and Miss Pinney 1911. Anasa has become, 

 so to speak, a classic animal. As the statements of earlier in- 

 vestigators did not completely agree, Professor McClung and 

 Miss Pinney made a careful reinvestigation. They had at 

 their disposal in part the material used by their predecessors. 



FIG. 36. A n a s a 

 tristis. A section of a 

 spermatogoneal cyst. 

 The peculiar arrange- 

 ment of the spindle is 

 characteristic. 



FIG. 37. Anasa tristis. Successive stages in the transformation of the nucleus of 

 a sexual cell (spermatogonium). The transformation is the preparation for the 

 development of the sexual element. After Edith Pinney. 



Their memoir is excellent, and I present a selection of their 

 pictures. We will consider first the commencement of the 



