The spermatozoa differ from those of other animals in having the form of cells which sometimes perform amoeboid movements.
Though possessing a complete copulatory apparatus and producing large quantities of spermatozoa, they have lost their sexual instinct and play no part in the economy of the species.
Spermatozoa and ova.
The spermatozoa exhibit many differences in shape, size and proportions, in the various groups of birds.
They contrast with those of the Oligochaeta and Hirudinea by reason of their frequently close association with the gonads, the same organ sometimes serving the two functions of excretion and conveyance of the ova and spermatozoa out of the body.
(as it appears) of the epidermis, and that it performs the function of a spermatheca is shown by its containing spermatozoa, or, in Stuhlmannia, a spermatophore.
In the most primitive condition the genital duct is single throughout its length and has a single external aperture; it is therefore said to be monaulic. The hermaphrodite aperture is on the right side near the opening of the pallial cavity, and a ciliated groove conducts the spermatozoa to the penis, which is situated more anteriorly.
Closed in a viscid secretion at the point where the albuminiparous gland opens into the duct intertwined with it; and on reaching the pcint where the spermathecal duct debouches they are impregnated by the spermatozoa which escape now from the spermatheca and meet the ova.
Fertilization takes place as the egg is laid, the spermatozoa being ejected from the spermatheca of the female and making their way to the protoplasm of the egg through openings (rnicropyles) in its firm envelope.
A series 750.) I, The longitudinal of sacs lined with an epithelium, the proexcretory canal; 2, one liferation of which gives rise to the ova of the tags containing the or spermatozoa, alternate between the flame-cells.
Spermatozoa, when mature, present no peculiarities.
As the animals become adult, diverticula arise on the tubes of these organs, which develop either spermatozoa or ova.
The protamines are a wellcharacterized class of albumins found in the ripe spermatozoa of fishes.
The ova and the spermatozoa 4.
Moreover, there is a significant agreement in the character of the spermatozoa of Limulus and Scorpio.
In Limulus Lankester found (15) the spermatozoa to possess active flagelliform " tails," and to resemble very closely those of Scorpio which, as are those of most terrestrial Arthropoda, are actively motile.
Lankester, " Mobility of the Spermatozoa of Limulus," Quart.
Coincidently, to allow of fertilization and the escape of excess of yolk, and of spermatozoa, other accessory ducts open at this point.
Thus in ectoparasitic Trematodes, the paired vagina transmits spermatozoa to the egg: and a canal carries off yolk from this point of junction either to the gut for resorption or to the exterior for exudation.
In these, the male organs ripen before the ova and spermatozoa may pass into the uterus before the external pore is formed (Looss).
In some Gymnolaemata, polypides which develop an ovary possess a flask-shaped "intertentacular organ," situated between two of the tentacles, and affording a direct passage into the introvert for the eggs or even the spermatozoa developed in the same zooecium.
In 1677 he described and illustrated the spermatozoa in dogs and other animals, though in this discovery Stephen Hamm had anticipated him by a few months; and he investigated the structure of the teeth, crystalline lens, muscle, &c. In 1680 he noticed that yeast consists of minute globular particles, and he described the different structure of the stem in monocotyledonous and dicotyledonous plants.
Insemination takes place either by the introduction of the penis into the cloaca of the female, or by the puncture of the bodywall of the female by the penis, and the injection of the sperm into the body cavity, whence the single spermatozoa must make their way to the eggs.
Angulata) have the sexes separate, and fertilization is effected in the open water after the discharge of the ova and the spermatozoa from the females and males respectively.
Hence, when he returns to organisms, it does not surprise us that he assigns to ova and spermatozoa cell-souls, to the impregnated ovum germ-soul, to plants tissue-souls, to animals nerve-souls; or that he regards man's body and soul as born together in the impregnated ovum, and gradually evolved from the bodies and souls of lower animals.
The spermatozoa enter it and pass through its walls and traverse a minute duct formed of two accessory cells, and finally enter the ripe ovum.
Ova are developed on the median, spermatozoa on the outer wall of each genital tube.
Sipunculoids are dioecious, and the ova and spermatozoa are formed from the modified cells lining the body-cavity, which are heaped up into a low ridge running along the line of origin of the retractor muscles.
The researches of Hoek have shown that in the same oyster the genital organs at one time produce ova, at another spermatozoa, and that consequently the oyster does not fertilize itself.
An oyster in this condition was kept in an aquarium by itself for a fortnight, and after that period its genital organs were found to contain multitudes of spermatozoa in all stages of development.
The oviducts may have diverticula serving as receptacles for the spermatozoa (in cases where internal impregnation takes place), and may be provided with glands secreting envelopes or shells around the eggs.
The male ducts often have glandular walls, secreting capsules or spermatophores within which the spermatozoa are packed for transference to the female.
It seems probable that in such cases the spermatozoa make their way from the adherent spermatophore through the body-wall into the body, and so by traversing the tissues reach the ovary.
The ovaries always contain spermatozoa, some of which project through the ovarian wall into the body cavity.
Spermatozoa are not found in the uterus and oviducts, and it appears probable, as we have said, that they reach the ovary directly by boring through the skin and traversing the body cavity.
In strong contrast with the condition in most Crustacea, the spermatozoa are mobile.
The spermatozoa have received a great share of attention, on the part not only of anatomists and physiologists, but even of systematic workers (40).
The spermatozoa of Discoglossus are remarkable for their great size, measuring three millimetres in length.
In the typical newts (Molge) of Europe, the males are adorned during the breeding season with bright colours and crests or other ornamental dermal appendages, and, resorting to the water, they engage in a lengthy courtship accompanied by lively evolutions around the females, near which they deposit their spermatozoa in bundles on a gelatinous mass, the spermatophore, probably secreted by the cloacal gland.
This arrangement facilitates the internal fecundation of the female without copulation, the female absorbs the spermatozoa by squeezing them out of the spermatophore between the cloacal lips.
The spermatozoa thus reach the eggs in the oviducts, where they may develop entirely, some of the salamanders being viviparous.