[Malformations in the head of the chick after treatment with TEM during organogenesis : II. Sensory organs and upper beak].

Malformations of various organ systems were observed in 10-day-old chick fetuses treated with single doses of the alkylating cytostatic agent TEM during organo genesis (31/2, 4 or 41/2 days after the beginning of development). The malformations occurring in the heads of the fetuses were examined microscopically. Whereas changes in the skeleton, musculature and nervous system were reported in part I (Scherschlicht, 1973), alterations in the sense organs and upper beak are discussed in part II below. The results of the whole study provide an inventory of the alterations occurring in head structures of chick embryos treated with single doses of TEM in three closely consecutive developmental phases. In all organ systems of the head, treatment-phase-specific changes appeared alongside changes not specific to the phase of development in which treatment was performed. These phase-specific alterations could serve as a basis for further detailed investigations, which should lead to an explanation of the role of proliferative rhythms in the differentiation of the organs of the head.Results 1. In the eyes irregularities of the stratification of the retina, coloboma of the retina and disintegration of the lens-bodies are prevalent, especially in embryos treated at 41/2 days of development; in embryos treated earlier they are absent or occur only to a very slight extent. 2. The changes in the upper beak (deformation of the nasal meatus and secondary palate, interruption of the cartilaginous nasal capsule, reduction of the bone rudiments, widening or narrowing of the palatal cleft) indicate a complex system of reciprocal interdependencies which must be considered in connection with the development of the embryonic processes in this region. The focus of the malformations appears to shift from the base of the beak to its tip, in relation to the age of the embryo at the time of treatment. 3. In the inner ear the development of the semicircular canals and of the cristae is inhibited. The semicircular canals (in particular the posterior canal) are mainly affected when treatment is performed at 31/2 days of development, but the cristae are altered almost exclusively when treatment takes place at 4 or 41/2 days of development. 4. In the middle ear malformations of the columella as well as a diminution of the tympanic cavity occur. This region is primarily affected by treatment at 4 or 41/2 days of development.