Large objects which propel themselves in air or water make use of inertia in the surrounding fluid. The propulsive organ pushes the fluid backwards, while the resistance of the body gives the fluid a forward momentum. The forward and backward momenta exactly balance, but the propulsive organ and the resistance can be thought about as acting separately. This conception cannot be transferred to problems of propulsion in microscopic bodies for which the stresses due to viscosity may be many thousands of times as great as those due to inertia. No case of self-propulsion in a viscous fluid due to purely viscous forces seems to have been discussed. The motion of a fluid near a sheet down which waves of lateral displacement are propagated is described. It is found that the sheet moves forwards at a rate 2π 2 b 2 /λ 2 times the velocity of propagation of the waves. Here b is the amplitude and λ the wave-length. This analysis seems to explain how a propulsive tail can move a body through a viscous fluid without relying on reaction due to inertia. The energy dissipation and stress in the tail are also calculated. The work is extended to explore the reaction between the tails of two neighbouring small organisms with propulsive tails. It is found that if the waves down neighbouring tails are in phase very much less energy is dissipated in the fluid between them than when the waves are in opposite phase. It is also found that when the phase of the wave in one tail lags behind that in the other there is a strong reaction, due to the viscous stress in the fluid between them, which tends to force the two wave trains into phase. It is in fact observed that the tails of spermatozoa wave in unison when they are close to one another and pointing the same way.

Analysis of the Swimming of Microscopic Organisms

Several aspects of salmonid sperm have been critically reviewed: structure, density, volume, chemical composition, metabolism, fertilisation techniques, motility, dilution, activation, storage at temperatures above and below 0deg; C and cryopreservation.

A review of the biology, handling and storage of salmonid spermatozoa

Multicellularity is characterized by cooperation among cells for the development, maintenance and reproduction of the multicellular organism. Cancer can be viewed as cheating within this cooperative multicellular system. Complex multicellularity, and the cooperation underlying it, has evolved independently multiple times. We review the existing literature on cancer and cancer-like phenomena across life, not only focusing on complex multicellularity but also reviewing cancer-like phenomena across the tree of life more broadly. We find that cancer is characterized by a breakdown of the central features of cooperation that characterize multicellularity, including cheating in proliferation inhibition, cell death, division of labour, resource allocation and extracellular environment maintenance (which we term the five foundations of multicellularity). Cheating on division of labour, exhibited by a lack of differentiation and disorganized cell masses, has been observed in all forms of multicellularity. This suggests that deregulation of differentiation is a fundamental and universal aspect of carcinogenesis that may be underappreciated in cancer biology. Understanding cancer as a breakdown of multicellular cooperation provides novel insights into cancer hallmarks and suggests a set of assays and biomarkers that can be applied across species and characterize the fundamental requirements for generating a cancer.

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Cancer across the tree of life: cooperation and cheating in multicellularity

Publisher Summary Knowledge of the physiology of fertilization of fish eggs seems to be most important not only for an understanding of the basic phenomena of fertilization in vertebrates but also for its bearing on fish culture. Sperm–egg interacting substances have been demonstrated in some fishes. Among these, the most evident is a factor localized in the chorion near the animal pole in the eggs of the bitterlings. The factor not only activates sperms but also attracts them by chemotaxis. The presence of the micropyle and its change play an important role in ensuring monospermy. Unlike echinoderm eggs, no sudden change of egg surface to protect the egg against polyspermy takes place. Dechorionated or denuded eggs always show polyspermy on insemination. The isotonic method of fertilization that is entirely satisfactory for the physiological analysis of fertilization reactions of the medaka, Orizias latipes , is presented. Fishes can be classified into four types with respect to the behavior of their ova in relation to salinity: (1) Orizias type, (2) Lampetra type, (3) Salmo type, and (4) Carassius type.

Physiology of fertilization in fish eggs.

9 – Sperm Chemo-Orientation in the Metazoa

Summary

i. The head of the sea-urchin spermatozoon is pear-shaped and axially symmetrical. The sub-microscopic morphology of the middle piece has not been investigated, but the tail, which terminates in an axial fibre, probably contains spiral or coiled structures, as in mammalian spermatozoa.



2. Spermatozoa of Psammechinus miliaris swim in spirals (frequency, 30–40 per sec), at an average translatory speed of 200/x/sec. at 18o C. This figure applies to very dilute suspensions. The spermatozoa of Echinus esculentus do not always swim in spirals.



3. The evidence in favour of sea-urchin spermatozoa being attracted by egg secretions is not conclusive. Experiments to settle this controversial question could be done without great difficulty.



4. Little is known about the metabolism of sea-urchin spermatozoa. The most important features are:



(a)No movement in absence of oxygen.



(b)Negligible acid production in presence or absence of oxygen.



(c)Over certain limits, oxygen consumption per spermatozoon an inverse function of sperm concentration.



(d)Cytochromes a, b, c, e and a3, succinic dehydrogenase, cocarboxylase, and catalase (in significant quantities) present.



(e)Endogenous substrate unknown, though possibly carbohydrate.



(f) Respiration inhibited by cyanide, and photo-reversibly by carbon monoxide.



A large number of substances, of widely different types, are said to stimulate or maintain the oxygen consumption of semen or spermatozoa. Among these are succinate, malonate, iodoacetate, copper, zinc, calcium, albumin and seminal plasma. The mode of action of these substances is in general obscure.



5. Sea-urchin spermatozoa contain a proteolytic enzyme which decreases the viscosity of gelatine, and desoxyribonuclease.



6. Sea-urchin spermatozoa contain or secrete three substances with characteristic chemical and biological properties. These substances and their principal characteristics are:



(a)Androgamone I. Not a protein. Inhibits sperm movement in certain circumstances.



(b)Androgamone II. Protein. Dissolves or precipitates egg jelly. Also called Antifertilizin.



(c)Androgamone III. Not a protein. Liquefies egg cortex. Sometimes called Sperm Lysin.



7. The spontaneously reversible agglutination of sea-urchin spermatozoa in the presence of egg secretions, and in particular of Gynogamone II, has a number of characteristics in common with serological reactions. In recent years this subject has been extensively studied and reviewed by Tyler (1948). Some of the more important conclusions are:



(a)Spermatozoa and G. II are multivalent with respect to their complementary combining groups, a condition which is responsible for the agglutination of spermatozoa in G. II.



(b)Multivalent G. II can be converted into a univalent form in which it reacts with homologous spermatozoa, but without causing agglutination.



(c)The sperm-G. II reaction exhibits the zone phenomenon (maximum agglutination when the two reactants are present in particular proportions).



(d)The sperm-G. II reaction causes a reduction in the fertilizing capacity of agglutinated spermatozoa.

Sea-urchin spermatozoa.

Fertilization in fish and lampreys has been the subject of important work, but this has not always received sufficient attention. One explanation may be that many of these studies have been published in somewhat inaccessible journals; another, that the plethora of papers on the eggs and spermatozoa of sea-urchins has hypnotized many of us into believing that the gametes of other animals are less suitable material for study. The purpose of this article is to give an account of fertilization in fish and lampreys, in a form which it is hoped will facilitate comparison with other animals.

Lord Rothschild

Papers

Sea-urchin spermatozoa.

Fertilization in fish and lampreys