Fertilised egg

The formation of these membranes from the fertilised egg in the Cyclophyllidea is shown in Fig. 7.4. Their structure and formation in Hymenolepis is considered in further detail on p. 179 their histochemistry is shown in Tables 7.3 and 7.6. In considering the functional morphology of eggs, it must be borne in mind that some eggs, such as those of the Pseudophyllidea (e.g. D. latum), hatch in water others hatch in the alimentary canal of invertebrates or vertebrates (e.g. H. diminuta, T. saginata) and one species (H. nana), uniquely, can hatch in both its intermediate (beetle) and definitive (rat) host. 

With the advent of the cell theory, embryonic growth was immediately accounted for by a sequence of cell divisions. A fertilised egg becomes 2 cells, and then 4, 8, 16, 32, 64 and so on. With 10 divisions the cell number is about a thousand, with 20 is a million, with 30 is a billion, with 40 is a thousand billion, and so forth. For the... 

The interesting point is that this is a mathematical version of the problem that we face in embryonic development. The fertilised egg contains far less information than the adult organism (whatever criterion is used to measure information in biological systems), and embryonic development can be described therefore as a process that is reconstructing a structure from incomplete information. This is another way of saying that embryonic development is a process that increases the complexity of a living system. The reconstruction of structures from incomplete information, in short, is a model that could help us understand how it is possible for a system to obtain a convergent increase of complexity. 

The gametes copulate in the gastrointestinal canal of the mosquito. The fertilised egg goes from the intestinal canal to the saUvary glands, where, via intermediary stages, they ripen to sporozoids and the circle is completed. 

In a series of careful studies, the anaesthetic effects of 30 barbiturates on the fertilised eggs and larvae of Arbacia pmctulata were quantitatively determined as a function of extra- and intracellular pH [160], The concentrations of undissociated barbituric acid derivative and its corresponding anion required to produce a 50 per cent reduction in rate of cell division of eggs and cessation of movement of larvae were calculated from the total concentrations of drug, its p/f under the conditions of the experiment, and the pH. The required concentration of undissociated species for a given compound was found to be very nearly constant over the pH range of the experiment, whereas the anion concentration varied considerably. This is exemplified in Table 3.3 for phenobarbitone pK a = 7-26). The results indicate very clearly that the barbiturates penetrate the cells only in the... 

The hypnotic barbiturates are capable of causing a fully reversible inhibition of cellular functions in simple organisms. They can, for example, inhibit cell division of fertilised eggs of the sea urchins (Arbacia punctulata), and movement of the larvae of the marine worm Arenicola cristata [160]. The blocking effects occur at or before the eight cell stage, and produce no immediate lethal effects. Complete recovery occurs when the eggs are returned to normal sea water after 2 hours or less, of exposure to the barbiturates. 

KDN has been shown to exist in its free form in the fertilised eggs of salmon.52 Examination of the cell wall of the green alga Tetraselmis striata has revealed the presence of 3-deo qr-Iyxo-2-heptulosaric acid [previously isolated from another source (Vol 22, p. 165)], and the 5-O-methyl ether of KDO, the first such methylated derivative found in nature, together with KDO itself. 53... 

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