Relationships between size of hypostome and number of tentacles in hydra

Abstract

AbstractPlots of the circumference of the hypostome of hydra against the number of tentacles surrounding each hypostome gave a linear relationship. The slope of the line is a characteristic of each species and strain of hydra studied and represents the amount of the circumference of the hypostome relegated to each tentacle. We interpret the intercept on the ordinate of such plots to represent the minimum amount of tissue needed, expressed as circumference of that hypostome, before a first tentacle can form. Hypostomes of newly dropped buds have about the same circumferences as those of adult animals. Diagrams of spacing patterns of tentacles from different species illustrate that the larger the animal, the greater the space between the tentacles. Intertentacular space occupies from 22 to 37% of the hypostome circumferences. The relationship between the average size of the hypostome for a number of groups of hydra and the average size of an animal (measured in micrograms of protein per animal) shows that the size of the hypostome is proportional to the size of the group of hydra being measured, with larger species of hydra having larger hypostomes until a maximum size is reached. We noticed a similar relationship between the part of the circumference of the hypostome occupied to each tentacle vs. animal size. Apparently more hypostomal tissue is allotted to each tentacle in specimens of larger species than to those of smaller ones, and the amount of hypostomal tissue per tentacle reaches a limit regardless of the size of the species.