ABSTRACT
Semper’s organ has been studied and compared in two genera, Limax and Helix. In both cases the organ, which lies on each side of, and beneath, the buccal mass, is composed of glandular elements surrounding ganglia; the latter originate from two nerves arising from each side of the cerebral ganglia. In both, the organ produces the external swellings that form the mouth lobes on each side of the head. The chief difference between the two is that Semper’s organ is much larger in Limax. In Helix it is reduced to strands of secretory and nervous tissue, dispersed among abundant muscle-fibres.
In H. aspersa the glandular area surrounding the ganglionic part of the organ is composed of three cell-types. The cytoplasm of the chief cellular component, ‘Semper’s’ cells, contains a number of lipochondria, some of which possess the cortex of concentric lamellae typical of phospholipid globules. The cytoplasm of the second cell-type, or ‘mucus’ cell, is filled with electron-lucent globules between which are scattered electron-dense bodies that contain some polysaccharide and lipid. The third cell-type, the reticulate cell, is rather similar to the mucus cell, except that its cytoplasm contains a reticulum formed by strands which lie within, or applied to, the electronlucent globules; these cells contain acid mucopolysaccharides. The structure of the mucus and reticulate cells bears certain resemblances to secretory cells in the sheath of the optic tentacles in the same species.
The function of Semper’s organ is discussed. Certain evidence suggests that some of its secretory cells may have an endocrine activity, and the significance of lipochondria in such actively secreting invertebrate cells is considered.
