Effect of insecticides (Dimiline WP 25, Torak EC 24 and Gamacide 20) on hydra (Hydra vulgaris Pallas).

Investigations showed that the three insecticides used had the most damaging effect upon hydra immediately after treatment. The tentacles and the hypostome are the parts most often damaged. Inse the affected cells, lesions appear in the intracellular membranes, the nucleus shell and the membranes of the mitochondria, Golgi complex and the endoplasmic reticulum, while the cell membrane is preserved. The damaged parts of the body regenerate within three days. Zymogen cells play a significant role in the course of regeneration. They dedifferentiate into gastrodermal interstitial cells and later into other types of cells of the ectoderm and the gastroderm. Apart from their intense participation in regeneration, these totipotent cells also invariably participate in the formation of new hydra buds. It was observed that Dimiline WP 25 and Torak EC 24 in the concentrations used stimulate asexual reproduction of this animal.

Regeneration of hydra damaged by zolone PM insecticide.

The zolone PM (phosalone) insecticide in the suspensions used destroys parts of the hypostome, ruins many buds and budless hydras. In the insecticide suspension a hydra shrinks and assumes the smallest surface. It is due to this that the surface mucous layer thickens and epidermal and gastrodermal cells become highly squeezed together. The insecticide penetrates the hypostomal opening and destroys hypostomal cells but does not act specifically upon a certain type of cells. Gradually, other cells replace the destroyed ones. They arrive from the gastrodermal region. Among them, zymogen cells, capable of differentiation und dedifferentiation into other types of cells, play the most significant part.

Effects of ultraviolet light (2535 A) and dactinomycin upon hydra (Pelmatohydra oligactis).

Hydras exposed to ultraviolet light (2535 A, 12 erg/mm-2/s-2) for 15 minutes suffer a depression immediately, individuals that survived recover quickly and lastingly. Hydras treated with dactinomycin of specific concentrations do not suffer a depression until several days later, do not recover and die eventually. The results are also comparable when hydras are exposed to light and treated with cytostatic of such concentration. In even milder solution of dactinomycin all unexpected hydras recover and survive. But, almost all of the hydras exposed to ultraviolet light and treated with this solution die eventually. The effect of ultraviolet light upon them is then distinctly adverse. Buds are much less damaged and they do not die in this concentration. They grow and reproduce normally. This paper deals with the above mentioned phenomena.

Elimination of zymogen cells and their derivates in Hydra.

Budles and one-budded hydras were exposed to action of antimite (N-methyl-bis-chlorethylamine hydrochloride, Pliva, Zagreb) in 7 mg/150, 7 mg/200 and 7 mg/250 ml concentrations. All these concentrations caused exterior morphological and cytological changes of the hydra body. In the ectodermal layer interstitial cells gradually disappeared, and then followed enidoblasts and enids. The discussion deals with interstitial cells in a normal untreated animal and possible differentiation of these cells in enidoblasts and enids after the action of antimite. Antimite prevents mitosis, but it does not stop differentiation of some of the cells into other cell types. In the gastrodermal layer the greatest changes which are caused by this cytostatic can be seen on zymogen cells. Their shape, cell structure and position in the gastroderm is changed. The results show that zymogen cells after the antimite action have a limited ability of dedifferentiation into gastrodermal interstitial cells, and that their ability to differentiate into mucous cells lingers a longer time. This depends upon their age. Only the hydras which were acted upon by such a dose of antimite that does not prevent division at last some of the zymogen cells can survive and wholly continue their development.

Regeneration of proximal and distal part of hydra body cut in the middle of gastral cavity and treated with dactinomycine.

Hydras were cut in the middle of the gastral part of the body. The part with the hypostome is marked as H, and the one with the foot as P. Both parts were treated with actinomycine D in 0,5 mg : 200 ml water solution. H-parts are much more sensitive to the effect of actinomycine than P-parts, and P lives considerably longer. It is supposed that such reaction are the result of specificity of H and P cell composition, and of the growth direction which is characteristic of hydra in general. H-part has a proportionally greater number of differentiated cells and this relatively smaller number of non-differentiated cells is spent in it quicker than in P-part in which they are more numerous. The growth direction has a decisive influence on further life of H- respectively P-part. Namely, H- in growth direction does not have any damaged body regions (hypostome and tentacles are intact) and it lacks the amputated P-part i.e. gastral region with foot: the region which is on the opposite side of growth direction of hydra. H-part has all the characteristic cells of this body region, so after amputation mostly it does not change. Unfavourable effect of citostatic manifests sooner and H-part desintegrates quicker. On the contrary, P-part lacks the hypostome with tentacles, and these are the body parts in the growth direction. Zimogen cells can dedifferentiate and differentiate. The hypostome and tentacles regenerate as far as is allowed by actinomycine.

Effects of dactinomycine (actinomycine D) on budless hydra and during its budding process.

The effect of dactinomycine (actinomycine D) is manifested in various ways, which depends upon its concentration and animal condition at the time of treatment. Dactinomycine is citotoxic in stronger concentations so hydra dies quickly. In thinner concentrations it stops the mitotic activity of the cell, but the basic metabolic processes continue as before. Interstitial cells differenciate into cnidoblasts for some time, the cnid production is not halted, but all of these cells disappear as well as zimogen cells which dedifferentiate into gastrodermal interstitial and into mucous cells. Such animals live longer but die eventually. The effect of dactinomycine is generally milder on animals with a larger cell mass, in hydras with the budding tendency where exist such reserves and in those hydras in which the budding process has begun. In these a part of mobile undamaged zimogen cells can remain. They keep their reproduction ability. These animals can survive and keep on growing normally.

Regeneration of proximal and distal body part in hydra exposed to ultraviolet light (2535 angstroms).

Pelmatohydra oligactis was amputated in the central part of the gastral region and exposed to radiation of ultraviolet rays (2535 angstroms, 12 erg mm(-2)s(-2) for 7, 15 and 20 minutes. The regeneration of the proximal and distal part of the animal which was fixed 8, 24, 48, 72 and 96 hours after the cutting and radiation has been studied cito-histologically. The regeneration of the wounds caused by cutting and those caused by radiation have been compared. It has been found out that the wounds caused by radiation heal much harder and that the radiation-destroyed hypostome needs a longer period to regenerate than the cutting-removed hypostome. It is assumed that radiation-destroyed parts have an inhibitory effect upon environment. But, cito-histological changes concord to a great degree in both cases. The foot regeneration in the animals cut and exposed almost entirely concords the regeneration in the control animals which were cut but not exposed. Namely, both of them, as a rule, remain permanently without a foot. In the paper we have tried to explain these results and brought out the conclusion that hydras do not regenerate the foot because in the bud region there are many zimogen and interstitial cells which are not characteristic of a foot and that is why hydra has a directed growth exclusively toward the distal part, never the opposite. The growth is localized to the hypostome and the bud region. Radiation does not inhibit the process of the budding that has already begun. It is assumed that undamaged cell material travels from the gastroderm toward the bud and serves its formation.