No. 3] THALASSEMA AND ZIRPHAEA. 615 



scatter some distance on each side of tlie equatorial plane, the 

 result is by no means a compact and sharply defined "plate," 

 as in the second polar spindle. The telophase (PI. XXXII, 

 Fig. 30) shows the chromosomes aggregated in a mass at each 

 pole, and the commencing cytoplasmic division. The latter, 

 however, may be retarded (PI. XXXII, Fig. 31), or even fail 

 to occur, in which case the two chromatin bunches remain at 

 the poles (PI. XXXII, Fig. 29). The centrosomes were only 

 occasionally to be made out at telophase. Not infrequently in 

 these stages a number of dark-staining bodies were observed in 

 an equatorial position (PI. XXXII, Figs. 30, 31) in all respects 

 similar to those figured by Korschelt in Ophryotroclta ('95), and 

 considered by him to be chromatin particles left behind in the 

 anaphase. 



After this division the three polar bodies remain clustered 

 together, and may attempt the formation of resting-nuclei. In 

 the two-celled stage one or more of them is to be found between 

 the blastomeres (PI. XXXIII, Fig. 46), evidently there under- 

 going degeneration and absorption. One or two centrosomes 

 pass into the second polar body; but I have not observed the 

 latter to divide or commence any of the initial stages. 



A mitotic division of the first polar body is a very common occurrence, 

 and has been repeatedly observed by previous investigators, though few 

 attempts have been made to follow out the process in full detail. This is 

 no doubt due to the minuteness of the elements and the often abortive 

 nature of the mitosis. The earliest reference to a division of the first polar 

 body appears to be attributed to KoUiker in 1852 (Fick, '93). Hertwig 

 ('77) describes the phenomenon in the leech Nephelis, though unable to 

 make out the behavior of the nucleus. From the mention of vacuoles that 

 fuse into one, we are led to infer that a resting-nucleus is formed or attempted. 

 No spindle nor centrosomes are figured. Trinchese ('80) observed the 

 viitosis of the first and also of the second, as did also Blochmann ('89) in 

 the honey bee, and Nussbaum ('89) in Pollicipes. Blochmann ('82) gives 

 a very complete account in A^eretina. He figures a spindle in metakinesis 

 lying paratangentially with its axis in the direction of the greatest diameter 

 of the body. No distinct centrosome is demonstrable. The chromosomes 

 are described as uniting into " ein solider Kern." The anaphase with Ver- 

 bindungsfaden is figured and also the cytoplasmic division. Platner ('86) 

 finds the division of the first a constant occurrence in Arion, giving three 

 bodies into which spermatozoa sometimes enter. He observed a spindle in 



