Electron microscopic study on the structure of septate and comb desmosomes

Summary An electron microscopic study of the desmosomes of Pelmatohydra oligactis and the silkworm (Bombyx mori L.) demonstrates that these two species of invertebrates have two different kinds of desmosomes. The term septate desmosome is applicable only in the case of the Pelmatohydra desmosomes, while a new term, comb desmosome (Danilova, 1968a, b), is suggested for the insect type. Differences in the structure of these two desmosome varieties can be detected only in tangential sections.In Pelmatohydra, two patterns of septate desmosomes are to be observed in ultrathin sections, yet this difference is due to different directions of the section planes. A scheme to show the structure of the septate desmosome of Pelmatohydra and that of the comb desmosome of insects is presented, as are some variant structures of these desmosomes in sections made in various directions. Globular subunits 30–40 Å in diameter have been detected in the hydroid septa.Fixation with potassium permanganate has failed to reveal any desmosome septa or combs. This observation supports the opinion that septate and comb desmosomes are of non-membranous nature.