Pseudoscorpions: Unusual Courtship in Invertebrates Pseudoscorpions are arthropods in the order of Pseudoscorpinadea. These are a group of small arachnids, such as spiders, mites, and ticks, that look like scorpions but do not have the scorpion's tail and sting. Even though the sexes in these creatures look very similar, they have complex courtship displays. The male in some of these species will drop a sperm bundle or spermatophore, which is often in the shape of a stalk, onto the ground. The female is attracted to this either by some chemical in the deposit or by a strand of silk left by the male. The female situates herself on top of the spermatophore and admits it into her own body through her genital opening. There are other species where the male steers the female to the spermatophore and helps her to position herself above it. He does this by grabbing her pedipalps. These are small appendages that resemble pincers with poison glands at their tips. The male pushes and vibrates against her to help in the reception of the sperm into her body. After the successful transmission of the sperm into her body, the female is ready to produce eggs. At this point, the female in several species of spiders will devour the male simply for nourishment. Although this is quite a common practice in spiders, the black widow is renowned for it, hence the name. This carnivorous mating behavior is not uncommon in nature. The female praying mantis, which is not an arachnid, does the same with its mate.
The Primate Brain Primates, the order of animals that includes monkeys, apes, and humans, contains species that show a higher level of brain development than most other mammals. Primate brains, especially in humans, are among the largest in the animal kingdom, compared to the body size of the animal. The primate brain retains in its structure the earlier forms and functions that have developed in lower vertebrates over evolutionary time, such as the brainstem and limbic system, but higher areas give new and more complex possibilities for learning and behavior. Because humans are upright, bipedal walkers, the human brain is at the top of the spinal cord rather than somewhat in front of it as in other primates. The human brain weighs only about three pounds, or about 2 percent of the weight of a 150 pound individual, but that is still larger relative to body size than the brains of other primates, even chimpanzees. The cerebrum makes up about 87 percent of the volume of the brain, and the cerebellum occupies most of the remaining volume. The diencephalon and brainstem in primates are relatively smaller than in most other mammals, compared to the entire brain size. The cerebral cortex in humans contains only six layers of cell bodies in the gray matter on the surface of the cerebrum. Many axons extending down from these cell bodies into the underlying white matter crossconnect the neurons that receive stimuli, process information, determine responses, and store memories. Specific areas of this cerebral cortex determine the body's voluntary muscle actions, or receive and analyze sensory information from the skin, muscles, and joints. Other cortical areas process incoming information about smell, taste, vision, and hearing, and compare those sensations to previous memories or store them as new memories. The most "human" aspect of the brain is the prefrontal cortex of the cerebrum, where logical analysis, predictions of the results of specific actions, and social interactions take place, although even in monkeys and apes the front of the brain manages social awareness and behavior. Since the primate brains of apes and monkeys are so similar to those of humans, many studies of brain function have involved experimentation on these animals, humans' closest relatives. Other mammals such as mice, rats, cats, and dogs have also served as subjects of brain studies that can be related not only to their own specific behavior, but also to how the human brain works in its various component parts. Since neurons are very similar to each other, whether they come fromsea slugs, squid, or mammals, experimentation using these animals has produced insight into how all brains and nervous systems work.
