A method is presented by which the sampling variance of all heritability estimates derived from ratios involving variance components may be found.

The ciliary feeding mechanism of Amphioxus (Branchiostoma bermudœ) is dependent for its continued effectiveness on the cleaning action of a powerful current of water produced by movements of the floor of the atrium. As ciliary feeding progresses, the buccal cirri become heavily choked with particles of detritus, and the feeding current entering the pharynx is thereby reduced. When this occurs, the atrial floor is violently raised and lowered, and water is pumped in and out of the atrium by way of the pharynx and oral hood, dislodging the accumulated particles from the buccal cirri. As is to be expected, the atriopore is capable of being closed during this process.

The mature Ptinid sperm examined under the light microscope is found to be specialised in that the chromatin is not contained within a sperm head but is distributed along a central axis. The migration of chromatin resembles that found in Coccids by Hughes-Schrader (1948). Surrounding the axis is a more flexible helical membrane extending the whole length of the sperm.

Under the electron microscope the membrane appears to consist of eighteen or twenty thin fibres and two thick fibres with striated sheaths. Near the posterior end of the membrane the fibres are surrounded by a ring. The structure is simpler than that of mammalian and avian sperms examined by other workers with similar techniques. Under the electron microscope, stages in the migration of chromatin in the immature sperm show a number of discrete opaque bodies which may be chromosomes. The approximate dimensions of the various structures are given.

The birthcoats of both coarse and fine-fleeced sheep can be separated into different types of fibres. Each type of fibre is formed by a particular type of follicle. The ratios of the different types of follicles are the same in all the breeds of British sheep studied, and therefore variation of the follicle population can be excluded as a factor in the evolution of the British types of fleeces. Some birthcoats are coarse, others are fine, and some birthcoats are short, others long. The two differences are independent both developmentally and genetically. In the few lambs studied, the coarse type is dominant over the fine type, and the short type is dominant over the long type. It is suggested that the Down shortwool fleece evolved along a different route from that which gave rise to the Merino shortwool fleece.

The branchial apparatus of Lampetra fluviatilis has been studied to find out whether the inspiratory movement is brought about by muscular contraction. Differences between existing accounts of the anatomy are pointed out, and a description is given of diagonal muscles which span re-entrant curves of the gill bars. Extirpation and stimulation experiments provide evidence that none of the available muscle groups can have an inspiratory function. The pressure changes in the gill sac indicate that the momentum of the water-stream in forceful expiration leaves a region of low pressure which initiates the inspiratory flow.