This paper presents a light microscope study of the cytology of the cells which secrete a substance into the lumen of the spermatheca of Rhodnius prolixus. On the basis of histochemical tests, the material in the lumen appears to be a mucoprotein or glycoprotein. It is suggested that the secretion provides a source of energy for the maintenance of the spermatozoa.
Gastrothylax elongatus, G. synethes, G. cobboldii, Ceylonocotyle streptocoelium, C. scoliocoelium, and Ceylonocotyle gigantopharynx are reported from domestic ruminants of Borneo. C. gigantopharynx is a new name for Paramphistomum gotoi of Dawes, 1936 (not Fukui), redescribed here on the basis of median sagittal sections to permit its placement in the taxonomic system of Näsmark.
There is evidence which suggests that the polarity of regeneration in hydra is determined by axial gradients of some sort. The mechanisms which may be involved in the establishment and maintenance of the gradients have been investigated by studying the reversal of polarity in graft combinations.
Complete polarity reversal can be effected by a grafted hypostome or by a grafted hypostome and peduncle. Partial polarity reversal can be effected by a graft of a peduncle only. Changes in regional properties associated with polarity changes have been investigated using isolation and transplantation techniques.
The experimental results suggest that the axial gradient behaves as a gradient of a substance. Such a gradient could be produced by either (a) simple diffusion of a substance from a source or (b) unidirectional transport of a substance plus back-diffusion. Some of the experimental results are incompatible with mechanism (a). All the experimental results are compatible with mechanism (b).
Some of the problems raised by the interpretation of the axial gradient in terms of a polarized transport model are briefly discussed.
The work described in this paper is concerned with the role of cell multiplication and cell movement in relation to the initiation of buds in hydra.
Hydra starved for 6 days do not initiate new buds; in such animals the mean mitotic index is only 10% of that in well-fed animals. When starved animals are re-fed, there is a rapid rise in mitotic index which reaches a maximum 12 h after feeding and thereafter declines. This cell division causes an increase in the cell population of about 30% in the 24 h following the meal. New buds are initiated at 24–72 h, i.e. at some time after the major part of the cell multiplication.
Cell division occurs in all parts of the axis to more or less the same extent and there is no sign of a growth zone in the budding region. However, the cell population in the budding zone of re-fed animals shows a significantly greater increase than in other parts of the axis and this can only be accounted for if it is assumed that cells have moved into this region from other parts of the axis.
Some cell multiplication is a necessary prerequisite for bud initiation, but grafting experiments with starved animals suggest that division per se is not necessary; the important factor seems to be the increase in size resulting from division.
The mechanics and causes of the cell movement which results in bud initiation are briefly discussed. It is suggested that changes in intercellular adhesion may be important.
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