234 KATHARINE FOOT AND E. C. STROBELL. 



EXPLANATION OF PLATES. 



All the photographs were taken with a Zeiss Apo. 2 mm. immers. lens, 140 apr. 

 and compensating ocular 4. Photos i to 31 are from smear preparations stained with 

 a saturate solution of Bismarck brown. In all these preparations the whole nucleus 

 is shown. 



Magnification of Photos i to 10 inclusive, 1,000 diameters. 



Magnification of Photos 1 1 to 32 inclusive, 600 diameters. 



As some of the germinal vesicles were too large to be included in the field at a 

 magnification of 1,000 diameters, we used a magnification of 600 diameters for all 

 the oocytes, in order to facilitate a comparison. 



The reproductions were made by the Holograph Company from our own negatives. 



PLATE I. 



Euschistus variolarius. 



PHOTO i . Two young resting spermatocytes, first order, one showing two nucleoli 

 and the other one nucleolus. 



PHOTO 2. A little later stage than Photo i. Two nucleoli are shown, unequal in 

 size, but this inequality is not so marked as in the two nucleoli of Photo 6. 



PHOTO 3. Resting first spermatocyte about the same stage of development as 

 Photo 2. One nucleolus present. 



PHOTO 4. A resting first spermatocyte showing two nucleoli about equal in size. 



PHOTO 5. A resting first spermatocyte with two nucleoli, unequal in size, though 

 the inequality here is not so conspicuous as in Photo 6. 



PHOTO 6. A later stage than Photo 5. Thechromatm shows the segregation 

 which precedes the formation of the chromosomes. Two nucleoli are present, very 

 unequal in size. 



PHOTO 7- First spermatocyte with the chromatin somewhat more closely segre- 

 gated than in Photo 6. One nucleolus is present showing a typical vacuole. 



PHOTO 8. A larger first spermatocyte with one nucleolus, the disposition of the 

 chromatin suggesting a network. 



PHOTO 9. A first spermatocyte showing an early stage in the formation of the 

 chromosomes ; one nucleolus is present. 



PHOTO 10. A much later stage than Photo 9. The bivalent chromosomes are 

 formed, but the number is not so clearly demonstrated as at later stages. (These later 

 stages, as well as the transitional stages, between Photos 9 and IO, are reserved for 

 a subsequent publication. ) The nucleolar-like thickening in the loop of the chromo- 

 some on the lower periphery of the group is not a small nucleolus. In the prepara- 

 tion it can be plainly recognized as a segregation of chromatin at the point where a 

 loop of the chromosome brings two parts of the thread in contact. Similar, though 

 less conspicuous thickenings are seen at other points where two threads cross. One 

 clear nucleolus is present in this spermalocyte. 



PHOTO II. Nucleus of a young oocyte, with the chromatin granules quite evenly 

 distributed throughout the nucleus. No nucleolus present. 



PHOTO 12. A slightly older germinal vesicle, with the chromatin segregated into 

 clumps, too numerous to represent individuual chromosomes. 



