READING IN CLASS
Read the text and say what information it carries.
Methodological guidelines on tasks
Notice the way in which the animal crawls upon the bottom. Is it well protected from enemies? Examine it carefully for parasites and for animals that are attached to it. Disturb it and see if it will swim. The animals are usually quite active in the evening, and if you visit a car in which they are kept, at this time of the day, you are likely to find them crawling up the sides, falling over and swimming on their backs. In this position it is easy to determine how they swim. The animals are very hardy and will stand even complete removal from the water for days at a time. During the spring and early summer, eggs are deposited in the sand; the male holding to the edge of the abdomen of the female with claws modified for the purpose, is dragged after her. If possible, the method of egg deposition and fertilization should be observed.
- The animal consists of a hoof-shaped cephalothorax, an abdomen, and a caudal spine. How are these joined? Is there any indication of segmentation of any of them?
- Examine the eyes with a lens and see that they are compound.
- On the lower side of the cephalothorax notice the appendages. Are they all built on the same plan? Compare them in male and female. Do you know what the modifications are for? Compare the pincers with those of a lobster. The first pair of appendages is called the chelicerce. Between the bases of the last pair of walking legs are the chilaria. Behind the chilaria is the operculum. Does this show evidence of being modified appendages? What is its function?
- Between the bases of the cephalothoracic appendages is the mouth. Do the bases of the appendages show any modifications that may serve as teeth? Can the pincer-bearing appendages be so bent as to be used in feeding?
- Along the sides of the abdomen notice the movable spines. How many are there?
- Under the operculum are the gills. How many groups are there? Are they arranged in pairs? How are they attached to the body? Are they movable? What reason is there for moving them? Examine a bunch of gills, frequently called a gill-book, and see how it is formed.
- At the base of the caudal spine notice the anus. Make a drawing of the ventral surface.
Internal Anatomy. This shows no very special adaptation and can be pretty well understood by studying a longitudinal section of a small preserved specimen.
In such a section the following organs may be found:
- The dorsal extensor, the ventral flexor, and the leg muscles.
- The elongated tubular heart just beneath the dorsal covering, in the posterior end of the cephalothorax and the anterior end of the abdomen.
- The alimentary canal, consisting of the esophagus and the anterior and posterior portions of the stomach, which extends posteriorly without much change to the anus. The liver, which surrounds the stomach and fills the greater portion of the cephalothorax, sends its secretions to the stomach.
- The cerebral ganglia, near the bases of the chelicerae, and the ventral chain of ganglia should also be seen in satisfactory sections.
A drawing is desirable.
Living specimens of these animals are not usually available for laboratory study. They live for the most part concealed during the day in crevices and holes and are active at night. Their food is largely spiders and insects which are seized by the claws and killed with the abdominal sting.
- Into what* parts is the body divided? How many segments are recognizable? Which are the most freely movable?
- Look for eyes. Do you find any besides the large pair?
- Find four pairs of slit-like openings on the ventral side of the pre-abdomen. These are the stigmata, the openings of the lung-books.
- Find the following appendages:
- Examine the mouth. Are there any jaws? Is a labrum present ?
- Find the position of the anus. The terminal spine is pro-vided with a poison gland and serves as a sting. In the living animal, the post-abdomen is habitually carried over the back.
(a) The chelicerw. What is their structure and where are they placed?
(b) The pedipalpi. Compare them with the chelicerae and count their segments.
(c) Four pairs of walking legs. Count their segments and see if they are armed with claws.
(d) The comb-shaped pectines. Are they on the thorax or the abdomen? Their function is doubtful.
Make a drawing of the under side of a specimen.
EPEIRA. (Round-Web Spider.)
Examine the webs of different species of spiders and see how they are constructed. Do all of the webs have places for the concealment of the owners? Do all spiders seem to construct definite webs for the capture of insects ? How do spiders entangle insects in their webs? Do different kinds use different methods? What parts of insects are eaten?
By destroying webs that are occupied by spiders that are in convenient places for observation, the construction of new webs may be observed. Notice how the framework is laid and then how the threads are attached to the framework. Are any of the legs used in handling the thread ? Are spiders equally active at all times of the day?
Spiders' webs may frequently be seen floating in the air, especially in the late summer or autumn. By watching spiders that are on fences and bushes the formation of these threads may be observed. Watch such a spider and see if you can deter- mine the use to which the thread is put.
Capture a spider and watch it descend by a thread. Where is the thread formed? Does the spider hold to it with its legs? Keep taking the thread up so that the spider cannot reach the ground, and see if there is a limit to the amount that can be formed. When the spider starts to climb the thread see how this is done, and whether the thread is taken up as the animal climbs or is allowed to float free.
Find where spiders lay their eggs. Some carry them. If you can find a specimen with an egg-sac, see how it is carried and whether it will drop its eggs when frightened. Remove the egg-sac and see if the spider will accept it again. Open several egg-sacs and see if the eggs all appear to be in the same stage of development.
Study the movements of the animal and see how many of the appendages are used in locomotion. Are any of the appendages used sometimes for locomotion and sometimes for feeling?
Examine the external structure of Epeira.
- Into what parts is the body divided? Do both parts bear appendages?
- Look for eyes on the anterior end of the body. How many are there? Do they seem to be simple or compound? Determine whether a specimen can see.
- The following appendages should be found :
- On the lower surface of the abdomen, near its anterior end, are two slits, the openings into the lung-sacs or lung-books. They are respiratory in function.
- Just in front of the spinnerets is a minute median pore, the spiracle, that is often very hard to find. It is the external opening of a series of abdominal tracheae.
(a) The chelicerce or mandibles. Notice their structure and see that each ends in a sharp claw. The poison-gland discharges at the tip of this claw.
(6) The pedipalpi or palpi. How many segments have they? Examine their tips for claws. What are they apparently used for?
(c) Four pairs of legs. Are they all alike? Count the segments and examine their tips for claws.
(d) On the abdomen, three pairs of spinnerets. Notice their positions and see if they are segmented. Understand their function and whether they are all used at the same time. They are probably true abdominal appendages.
Make a drawing of a ventral view.