[
1980]
Nematodes have long been recognized to have peripherally located sense organs. These comprise modifications of the cuticle as papillae, pores, or setae associated with an underlying nerve process. However, their generally small size precluded any in-depth understanding of either structure or function. As recently as 1971 a review of nematode anatomy considered the nature and function of nematode sense organs within only three and a half pages. Only 5 years later, McLaren required 70 pages to review the same subject, primarily because of the recent contributions from electron microscopic studies. Although most of these studies were of animal parasites, similar studies of plant-parasitic species followed quickly, and in 1975 two major papers were published dealing with the free-living microbial feeder, Caenorhabditis elegans. This nematode has been extensively studied as a model system to investigate developmental processes, and, since it is small, it has been feasible to reconstruct with great accuracy the total cellular composition of various parts of its anatomy. These studies in turn allow us to reappraise others, especially those of the larger animal parasites where cell identities are often harder to trace. They have also shown that nerves are associated with internal tissues of the body in manners suggesting that they may monitor internal functions or detect external stimuli capable of penetrating body tissues. It therefore seems important to recognize two classes of sensory organs (1) cuticular or peripheral sense organs, and (2) internal sensory
[
Nature,
1988]
The classical view of embryogenesis in the nematode worm Caenorhabditis elegans has been that developmental decisions are almost entirely dictated by lineage, with little if any contribution from the cellular interactions that are thought to be crucial to the formation of the body pattern in other organisms. (A distinction that Sydney Brenner used to characterize as European versus American - Europeans being defined by their ancestry and Americans by their neighbors.) The notion of a pre-programmed cell-autonomous progression from egg to adult would seem consistent with the remarkable invariance of the worm body plan; but recent research has increasingly eroded the peculiar position of worms in the annals of embryology; and two papers on pages 547 and 551 of this issue illustrate how invariance may be achieved in one critical feature of nematode morphology by a combination of two cellular interactions that together decide the fate of the vulval