The Life-History of Hypotrichous Infusoria. 609 



in Gastrostyla there are four macronuclei similarly placed. The 

 macronuclei in all three species consist of at least two elements: 

 First, a substance, undoubtedly chromatin, having a strong 

 affinity for nuclear dyes; and second, a clear substance, resisting 

 all stains, which may be termed achromatin. The general appear- 

 ance of the nucleus is nearly homogenous though this is 

 probably caused by the massing of a granular matrix. A mem- 

 brane surrounds the nucleus and a very delicate commissure 

 apparently connects the macronuclei though it is very difficult to 

 determine. From time to time a Kernspalt is observable. Asso- 

 ciated with each macronucleus is a small spherical micronucleus; 

 in Oxytricha and Pleurotricha there are typically two, and in 

 Gastrostyla four, micronuclei. The staining reaction of the rest- 

 ing micronucleus is the same as that of the macronucleus. A 

 typical specimen of Oxytricha fallax is illustrated in Fig. 15. 



During the earlier part of the Oxytricha A-culture no prepara- 

 tions were made, so that during the first period of decline up to the 

 sixteenth ten-day period (Diagram I) I am unable to trace the 

 morphological changes. On April 2, 1902, however, two indi- 

 viduals of the 230th generation were preserved. A glance at the 

 photographs of these specimens (Figs, i and 2) shows that marked 

 vacuolization of the cytoplasm has occurred in each case. In 

 Fig. I the two macronuclei are considerably displaced in the cell, 

 and each shows a peculiar vacuolized condition of the nuclear 

 material, the chromatin being segregated about what appear like 

 bubbles of the achromatic substance. Each macronucleus is sur- 

 rounded by a clear area which separates it sharply from the 

 cytoplasm. I believe that this clear area is caused by an accumu- 

 lation of the achromatic substance against the nuclear membrane, 

 which thus produces the appearance of a halo about the nuclear 

 bodies. In this particular specimen there are two micronuclei 

 present, one being nearly invisible in the photograph as it is 

 somewhat below the plane of focus. Fig. 2 shows the same 

 condition of cytoplasm and nuclear material but the two macronu- 

 clei are fused and the whole mass is surrounded by the halo. 

 At least three micronuclei are present in the preparation, two of 

 which are visible in the figure, so that we have a case of micronu- 

 clear reduplication similar to that which Maupas described in his 

 culture of Oxytricha sp. Specimens from A-2 of the 239th genera- 

 tion (Fig. 3) and A-i of the 241st generation (Fig. 4) show a 



