Animal evolution. The end of the intermediate taxa?

Contrary to general belief, there has not been a reliable, global phylogeny of animals at hand within the past few decades. Recent progress in molecular phylogeny is rapidly changing the situation and has provided trees that constitute a reference frame for discussing the still controversial evolution of body plans. These trees, once purged of their possible artefacts, have already yielded confirmation of traditional, anatomically based, phylogenies as well as several new and quite significant results. Of these, one of the most striking is the disappearance of two superphyla (acoelomates such as flatworms, pseudocoelomates such as nematodes) previously thought to represent grades of intermediate complexity between diploblasts (organisms with two germ layers) and triploblasts (organisms with three germ layers). The overall image now emerging is of a fairly simple global tree of metazoans, comprising only a small number of major branches. The topology nicely accounts for the striking conservation of developmental genes in all bilaterians and suggests a new interpretation of the 'Cambrian explosion' of animal diversity.     

The genius of E. E. metchnikoff— Discoveries over the centuries

On the 15 of May we celebrated the 150th anniversary of the outstanding Russian biologist Elias E. Metchnikoff (1845–1916)—Nobel Prize winner (1908), full and honorary member of many scientific academies of the world. His main works were applied to the zoology of invertebtates, evolution, embryology, immunology, microbiology, infectious pathology, gerontology, etc. Elias Metchnikoff published essays on anthropology, theory of orthobiosis, role of social and social-hygienic factors in solving the problems of old age and life elongation. On 30 May-2 June 1995 an International Symposium dedicated to Metchnikoff's 150th anniversary was held in Moscow. This is a text of the lecture given by us at the opening ceremony.     

The ‘Embryonic moults’ of the milkweed bug as seen by the S.E.M.

Deposition, detachment and removal of the three embryonic cuticles are studied. The menbrane-like cuticle 1 covers the embryo during katatrepsis and ‘disappears’ thereafter. Cuticle 2 deposition starts shortly before dorsal closure. Its apolysis is accompanied by contractions of the embryo. Ecdysis of cuticle 2 takes place during hatching. Only cuticle 3 (= first larval cuticle) shows differentiations like sensilla and cornea. Peaks of ecdysteroid (and probably JH) titre are observed during apolysis of cuticle 1 and cuticle 2 (Dorn, 1981). Transition from ectoderm to epidermis proper takes place shortly before and during onset of cuticle 2 synthesis.     

The formation of vesicles in the developmental cycle of the nodular endophyte of Hippophaë rhamnoides L.

Summary The mature vesicle of the Hippophaë rhamnoides root nodule endophyte is spherical, approximately 3–4 m in diameter and exhibits a high degree of apparently random septation. Electron micrographs are presented which show that this vesicular form in the endophytic development within the host cell originates as a swelling of the hyphal tip. The young vesicle is non-septate and in general attains a minimum diameter of 3 m before septation becomes evident. The number of septa then increases with vesicle maturity.     

Thoughts of a travelling ecologist 12.The plight of the monarch butterfly

<正>Nature conservation needs people who care about nature,and the efforts to convince people to care about the fate of nature has extensively relied on selected charismatic species,the"conservation icons".One famous example is the great panda,Ailuropoda melanoleuca,well known as the World Wide Fund for Nature(WWF)logo.When it comes to invertebrates,the     

The pharmacology of the isolated foregut of the locust schistocerca gregaria—I. the effect of a range of putative neurotransmitters

1. Isolated locust foreguts exhibited little or no spontaneous contractile activity.2. Proctolin (10⁻⁹m-10⁻⁶m) caused rapid and powerful contraction of the tissue while the response to similar doses of l-glutamate was much weaker.3. 5-HT (10⁻⁸M-5 × 10⁻⁶M), acting at ketanserin-sensitive receptors, was the most powerful tissue relaxant tested.4. Relaxation caused by octopamine (10⁻⁷M-10⁻⁵M), acting at ketanserin-insensitive receptors was less than 50% of that caused by similar concentrations of 5-HT.5. ACh (10⁻⁵M-10⁻³M) induced relaxation, mimicked by nicotine and antagonised by d-tubocurarine, was seen only in the presence of the anti-cholinesterase neostigmine.