^>- in o> ^ o T- (O f^ CO Donated to The Department of Anatomy from the library of Professor James Playfair McMurrich M.A,, Ph.D., LL.D., F.R.5.C, Professor of Anatomy in The University of Toronto 1907 to 1930 > LABORATORY OUTLINES FOR EMBRYOLOGY H ARMAN LABORATORY OUTLINES FOR EMBRYOLOGY BY MARY T. HARMAN, PH.D. ASSISTANT PROFESSOR OF ZOOLOGY, KANSAS STATE AGRICULTURAL COLLEGE PHILADELPHIA P. BLAKISTON'S SOiN & CO. 1012 WALNUT STREET Copyright, 1914, by P. Blakiston's Son & Co. a'HE]>MAPIj£l«FRE}3S>70ItK«FA PREFACE These outlines were first written for use by students in the large laboratory classes in embryology in Kansas State Agricultural College, and represented the work done (by those classes) during one term (twelve weeks). After they were used for two terms, they were revised, parts rewritten, and some sections added. It is thought that the use of an outline is the simplest means of secur- ing more or less uniformity in the work of the several classes and, at the same time, of encouraging the devel- opment of the individuality of both the student and the teacher. The course is not intended as an independent one, but is planned to supplement recitation and lecture work so that the student may obtain by observation a general knowledge of the processes and phenomena of development. The material suggested for use in the course is such that, if it is not already at hand, it may be obtained v^-ith a minimum of difficulty. The work is meant to be so arranged that if time does not permit the use of all parts of the outlines, some sections may be omitted and at the same time preserve the continuity of the course. The author is indebted to various authors for sug- gestions. Those suggestions have been so modified from time to time that it is scarcely possible to give credit to VI PREFACE any single author for any particular part of the work. The following books, however, have been particularly helpful : The Development of the Chick, Lillie. Embryology of the Chick and the Pig, Lillie. The Development of the Human Body, McMurrich. Text Book of Embryology, Hertwig-Mark. Elements of Embryology, Foster & Balfour. Laboratory Text Book of Embryology, Minot. A Manual of Histology and Organography, Hill. Text Book of Zoology, Galloway. The Cell in Development and Inheritance, Wilson. The author wishes to express her gratitude to Dr. R. K. Nabours for his criticism of a part of the manuscript and to Dr. Paul S. Welch for reading and criticising the entire manuscript. Mary T. Harman. CONTENTS Cell Division i The Spermatozoan 3 The Egg 4 Fixed and Stained Embryos — The Chick 15 The Pig Embryo 32 Index 45 vu LABORATORY OUTLINES FOR EMBRYOLOGY CELL DIVISION 1. All organisms are composed of cells. The essential parts of a cell are: (i) The general cell substance, the cytoplasm, and (2) a highly differentiated nucleus. ]Most cells have a limiting membrane, the cell-wall. Animal cells may have one or more specialized bodies h'ing near or immediately inside the nucleus, the centrosome. The nucleus may be separated from the cytoplasm by a thin membrane, the nuclear membrane. The substance of the nucleus is composed of the chromatin material, which stains readily with certain dyes and the achromatin, which stains less readily. When the cell is in the so- called resting stage there is a portion of the chromatin which is larger, more compact, and stains more densely than the other chromatin granules. This is the chroma- tin nucleolus. There may be more than one nucleolus. Draw a cell in the resting stage and label the parts. 2. When division is about to take place, the chromatin elements in the nucleus have the appearance of a coiled thread, the spireme. The spireme is not always a con- tinuous thread. The nuclear membrane often disappears at this stage. 2 LABORATORY OUTLINES POR EMBRYOLOGY Draw a cell in the spireme stage and label the parts. . 3. The spireme becomes thicker and finally separates into a number of pieces called chromosomes. The chro- mosomes are of different shapes, depending upon the species of plant or animal. This stage is known as the astroid stage. If the cell is an animal cell, the centrosome has divided and the parts of it have migrated to opposite sides of the nucleus. From the centrosomes as centers, radiations extend out through the cell. Draw a cell in the astroid stage and label all the parts. The process up to this point is known as the prophases or preparation stages. 4. From opposite sides of the nucleus radiations ex- tend across it. These are known as spindle fibers. The chromosomes arrange themselves across the spindle mid- way between the poles. Each chromosome splits longi- tudinally into halves. This stage is known as the meta- phase or middle stage. Draw a cell in the metaphase and label all the parts. 5. One-half of each of the chromosomes passes along the spindle fibers to one pole and the other half to the other pole. When these chromosomes collect around the poles they have the appearance of a double star. This is called the diastroid stage. The diastroid stage and the stages in which the chromosomes are between the center of the spindle and the poles are known as the anaphases. Draw a cell with the chromosomes some distance from the poles. Label the parts. Draw a cell in the diastroid stage. Label the parts. SPERMATOZOAN 3 6. After the formation of the diasters the chromosomes unite to form a spireme at each pole. From this con- dition they change into the resting stage or reticular condition. Coincident with the nuclear changes, the cytoplasm may have become constricted into masses, or separated by the formation of a wall perpendicular to the axis of the spindle. The resultant masses are known as daughter cells. The daughter cells may move apart or remain in contact. These final stages are known as the telophases. Draw a telophase in which the chromatin is in a spireme (di-spireme). Label the parts. Draw two daughter cells. Label the parts. The cell has been followed through the process of divi- sion, known as karyokinesis or mitosis. As a result of this division there are two cells instead of one. Write out the description of the process of mitotic cell di\dsion from the resting stage to the daughter cells. THE SPERMATOZOAN With the high power objective examine the slide of the pig spermatozoa. Select a single spermatozoan. It is composed of two parts, a large ovoid head and a long fila- mentous tail. The anterior part of the head, the head cap, does not stain so intensely as the remainder of it:. At the base of the head is a part that stains ver\' in- tensely. This is the mid-piece. What is the com- parative length of the tail? Make a drawing of the spermatozoan and label all the parts. 4 LABORATORY OUTLINES FOR EMBRYOLOGY THE EGG An egg is a cell and has all the essential parts of a cell. However, in the egg, some of the parts have special names. The cell- wall is called the vitelline membrane; the nucleus is called the germinal vesicle; and the nucleolus is called the germinal spot. An egg differs further from most other cells in that it contains yolk material. This yolk material is called deutoplasm. I. Formation of an Egg Eggs are produced by special glands called ovaries. The ovary is covered by a layer of cubical cells called the germinal epithelium. It is from this germinal epi- thelium that the eggs are formed. Early in embryonic life, epithelial buds or strings of epithelial cells grow down into the ovary. Soon these buds lose their connection with the germinal epithelium and form small groups or nests of cells. These groups or nests of cells are known as young Graafian follicles. In each follicle one cell takes a central position and is destined to fo'^m the egg or ovum. The egg increases rapidly in size, receiving protection and perhaps nourishment from the cells which surround it. The cells which surround the egg are known as follicular cells. In the section of the cat ovary, find a young Graafian follicle, draw it, and label all the parts. Only a small number of the young ova ripen and are discharged as mature ova. Those which mature do so FORMATION OF AX EGG 5 in the follow-ing manner: The egg of the young Graafian follicle grows until it is a large spherical cell. The fol- licular cells remain small and multiply rapidly, forming two layers of cells, between which at one side of the follicle a cavity appears. This ca\dty is called the fol- licular cavity. As the follicle grows larger, this ca\'ity, which is eccentric in position, is filled with a fluid, the follictdar ftuid. The cells composing the layer of fol- licular cells, which immediately surround the egg, in- crease rapidly in number until there are several laj'ers. These cells are known as the discus proligerus. The cells external to the follicular ca\dty are the stratum granu- losiim. There are finally from eight to twelve layers of cells in the stratum granulosum. The discus proligerus is attached to the stratum granulosum. The lighter area immediately outside of the \Hltelline membrane is the area peUucida. The row of cells of the discus proligerus that radiates from the o\aim is the corona radiata. \Mien the egg with its surrounding tissue has reached this stage of development it is known as a ripe Graafian follicle. The follicle is enclosed by a capsule composed of two kinds of cells. Those cells which lie nearest the stratum granulosum are more or less spherical, and the others are rather elongate. This capsule is the iheca folliculi. Surrounding the theca folliculi and forming the sub- stance of the ovars' are long, fibrous cells, the stroma. In the section of the cat ovary, find a ripe Graafian follicle and draw it. Label all the parts. 6 LABORATORY OUTLINES FOR EMBRYOLOGY 2. Maturation a. While the egg is in the Graafian follicle the nucleus is large and the chromatin is in the so-called resting con- dition. The egg is said to be in the growth period. At the end of the growth period it passes through two suc- cessive, modified mitotic divisions, the maturation divi- sions. In the eggs of some animals the maturation divisions occur before the egg leaves the ovary, but in others they do not occur until afterward. The Ascaris egg is of the latter type. On the slide of Ascaris find an egg in the growth period. Draw it and label all the parts. \ b. At the end of the growth period, there are half as many chromatin masses as there are somatic chromo- somes. In Ascaris magalocephala hivalens there are four somatic chromosomes and, therefore, two chromatin masses at the end of the growth period. Each chroma- tin mass is made up of four parts and is called a tetrad. The tetrads arrange themselves on a spindle which is com- paratively small and is eccentric in position. Draw an egg with the tetrads in the middle of the spindle {metaphase) and label all the parts. c. Each tetrad divides into two parts called dyads. One dyad from each tetrad moves to one pole of the spindle and the other dyad moves to the other pole of the spindle. When the dyads reach the poles the egg divides. The resultant cells are very unequal in size. One cell con- tains half of the chromatin and little of the cytoplasm. FERTILIZATION 7 It is the first polar body. The other contains the other half of the chromatin and almost all the cytoplasm. It is the secondary oocyte. The first maturation division is now completed. Without any change in the form of the chromatin ma- terial, a new spindle is formed in the secondary oocyte. The first polar body may or may not divide. Draw a secondary oocyte in a metaphase stage and label all the parts. d. Each dyad di\'ides into tw^o parts called monads. One monad from each dyad moves to one pole of the spindle and the other one moves to the other pole of the spindle. Draw a secondary oocyte in an anaphase stage and label all the parts. e. When the monads have reached the poles there is a second unequal division of the egg. This division is similar to the first one. The small cell is the second polar body and the large one is the matured ovum. Draw a matured ovum showing the second polar body and label all the parts. 3. Fertilization In Ascaris the spermatozoan penetrates the v-itelline membrane before the maturation divisions occur. It may be seen in the cytoplasm of the egg either as an indefinite dark blotch or as unchanged in shape. After maturation is completed the chromatin of the egg changes into the so-called resting condition and is called the 8 LABORATORY OUTLINES FOR EMBRYOLOGY female pronucleus. Coincident with the changes in the egg nucleus, the spermatozoan also changes into the so- called resting stage and is called the male pronucleus. These two pronuclei approach each other and fuse to form ih& first segmentation nucleus. Draw a cell showing the male and female pronuclei. Label all the parts. 4. Cleavage The amount and distribution of the yolk is correlated with the character of the division of the egg {segmenta- tion, cleavage). In eggs, which, for the most part, are small and contain a comparatively small amount of yolk material {deuto plasm) , the segmentation is complete. That is, the whole egg divides into two daughter cells. This kind of cleavage is known as total or holohlastic cleavage. If there is a very small amount of yolk and this yolk almost uniformly distributed throughout the cytoplasm, the daughter cells, in general, are of uniform size. This kind of cleavage is known as equal cleavage. Examples of holoblastic equal cleavage are found in the Echinoder- mata, Amphioxus, and, in general, in the Mammalia. If the yolk is concentrated more at one pole than at the other and yet there is not a large amount of it, the cells resulting from segmentation are unequal in size. This kind of cleavage is known as unequal cleavage. Ex- amples of holoblastic unequal cleavage are found in the Cyclostomata and the Amphibia. In eggs where the amount of yolk is comparatively CLEAVAGE 9 large, segmentation is incomplete. This kind of cleavage is called merohlastic cleavage. The cytoplasm may be at one pole and the greater part of the egg composed of deutoplasm. In eggs ha\dng this distribution of yolk material, the process of segmentation is confined to the region of the cytoplasm and as a result there is formed a cellular disc. This kind of cleavage is called discoidal cleavage. Examples of meroblastic discoidal cleavage are found in the fishes, reptiles, and birds. In some eggs the nucleus lies at the center and when it di\-ides the nuclei thus formed migrate to the peripher\' and thus the yolk becomes surrounded by a layer of cells. This process is called peripheral cleavage. Examples of mero- blastic peripheral cleavage are found in a number of the Arthropoda. a. Holoblastic Cleavage (i) Equal Cleavage On your slide of the starfish eggs look for a single un- fertilized egg. The unfertilized egg may be recognized by its large and comparatively clear nucleus. These eggs are large enough to be seen with the naked eye. Examine one first with the low power and then ^^th the high power. How does the germinal vesicle compare in size with the w^hole egg? WTiat difference in structure do you observe between the germinal vesicle and the remainder of the egg? Locate the germinal spot. Draw an egg about one and one-half incites in diameter and label all the parts. Find an egg which has di\'ided. Can you find a lO LABORATORY OUTLINES FOR EMBRYOLOGY nucleus in each part? How does the nucleus here differ from the nucleus in the unfertilized egg? Draw a two-celled, a four-celled, and an eight-celled stage. Label all the parts. Make the drawing one and one-half inches in diameter. (2) Unequal Cleavage Examine a frog's egg that has not divided. One part of the egg is dark and the other part is light. The dark part of the egg is the animal pole; the light part is the vegetative pole. Is the pigment confined entirely to one part of the egg? Draw a lateral view of an unsegmented egg and label the parts. Make the drawing about an inch and a half in diameter. Shade in the pigmented part. Find a two-celled stage. How has the division plane divided the egg with reference to the light and dark portions? Is there any difference in the depth of the segmentation furrows? How do you account for it? Draw a two-celled stage, lateral view. Label parts. Study a four-celled stage. What is the relation of the second cleavage plane to the first cleavage plane? To the polls of the egg? How do the cells compare in size? Draw a four-celled stage, view from the animal pole. Label the parts. Study an eight-celled stage. What is the relation of the third cleavage plane to the other two cleavage planes? To the polls of the egg? What is the comparative size of the cells? CLEAVAGE II Draw an eight-celled stage, lateral view. Label the parts. Examine further stages of di\dsion. What is the relative size of the cells in the dark and light hemispheres? What is the relative number? Examine an egg in a many-celled stage. With a sharp scalpel or razor split the egg into halves through the poles. What is in the center of the egg? How many- layers of cells are there? When an egg has divided until there are many cells and these cells are arranged in a single layer so as to form a hollow sphere, it is called the blastula stage. The cavity in the center of the sphere is the segmentation cavity. Draw a section through a hlasttda and label the parts. Examine an tgg which has a small indentation on one side. Where is this indentation with reference to the poles? With a sharp scalpel or razor split the egg into halves through this indentation. How are the hemi- spheres of this egg different from the hemispheres of the blastula stage? WTiat is the form of the segmentation caiityhere? How many layers of cells are there? The cells at one pole di\'ide more rapidly than they do at the other pole, which results in the folding in of the cells at one pole. Which pole? This process is known as gastrulation, and the stage is kno\vn as the gastrida stage. The indentation, or the ca\dty thus formed, is called the archenteron or primitive gut cavity. The opening of the archenteron to the outside is called the blastopore. Draw a section of a gastrida and label the parts. 12 LABORATORY OUTLINES FOR EMBRYOLOGY 5. The Hen's Egg a. A Raw Egg Crack slightly the broad end of a hen's egg. Carefully pick off a small portion of the shell. Notice that beneath the shell there is a white leathery tissue. This is called the shell membrane. How many layers are there in the shell membrane? If the egg is not perfectly fresh, there will be a space at this end of the egg. This is called the air-chamber. Where is the air-chamber with reference to the shell and the membrane? Immediately beneath the shell membrane is the colorless albumen, the white of the egg. Pour the egg out into a saucer. Examine a piece of the shell with the dissecting microscope. Notice that it is filled with very small holes. What is the function of these holes? Notice that the white is not all of the same consistency. What is the location of the more fluid part ? From the opposite sides of the colored part of the egg, the yolk, extend two twisted chords called the chalazcB (hail stones). Are they attached to the yolk? Are they attached to the shell? The yolk is enclosed in the vitelline membrane. What other name could be applied to the vitelline membrane? If the egg has been fertilized, there will be at a point on the surface of the yolk, lying immediately underneath the vitelline membrane, a small white disc about 4 m.m. in diameter. This is the blastoderm. If the egg has not been fertilized, this spot will be much smaller. It is the nucleus and cytoplasm of the cell. The blasto- derm is composed of a layer of cells. The yolk, as in all eggs, is for the nourishment of the developing embryo. A HARD-BOILED EGG I3 Draw the egg as you see it in the saucer. Label the parts. Put a drop of the yolk on a slide, add a little water, and examine it with the microscope. What is the appearance of the yolk granules? Are they uniform in size? Draw some of the yolk. b. A Hard-boiled Egg Break the shell of a hard-boiled egg and remove with- out breaking the white. Observe, again, the air-chamber and the character of the shell and the shell-membrane. Try to peel off the white in thin layers. It will be seen that the white is arranged in the form of a spiral. What is the direction of the spiral? Where is the apex of the spiral? Peel off all the white. Usually the vitelHne membrane is also taken off from the yolk with the white. Observe the vitelhne membrane. On one part of the yolk there is a disc that is lighter in color than the remainder of the surface of the yolk. This disc is called the "nucleus of Pander.'^ With a sharp knife or razor cut through the "nucleus of Pander" in such a way as to divide the yolk into two hemispheres. If the egg is fresh, it will be seen that the ''nucleus of Pander" is connected by means of a narrow neck to a central portion of the egg composed of similar material. This is lighter in color and is more liquid than the other yolk. It is composed of the so-called white-yolk. The darker yolk material is called yellow yolk. It will be noticed that there are alternate layers of white yolk and yellow yolk. How many layers are there? WTiich 14 LABORATORY OUTLINES FOR EMBRYOLOGY layers are the thicker? Which forms the greater part of the yolk, the yellow or the white yolk? Draw the yolk hemisphere and shade in the yellow yolk. Label the parts. c. An Egg Incubated Three Days — Live Embryo Open the large end of an egg that has been incubated at least three days. Notice that in whatever position you turn the egg the embryo is on top. , Pour the egg into a dish containing normal salt solution which is about milk warm. How much of the yolk is covered by the blasto- derm? Notice that immediately surrounding the em- bryo is a light area. This is called the area pellucida. That part of the blastoderm extending beyond the area pellucida is the area opaca. The part of the area opaca which contains the blood vessels is the area vasculosa. What part of the area opaca is occupied by the area vasculosa? What is the shape of the heart? How fast does it beat? The vessels carrying the blood into the heart are the vitelline veins.- How many vitelline veins are there? The blood is carried from the embryo to the vascular area by means of the vitelline arteries. How many vitelline arteries are there? How does the blood get from the heart into the vitelline arteries? What is the shape of the embryo? What are the differences between the yolk of this egg and the yolk of the fresh egg? What are the differences in the white? Draw the embryo showing its relation to the yolk. Label the parts. FIXED AND STAINED EMBRYOS THE CHICK 15 FIXED AND STAINED EMBRYOS— THE CHICK I. Embryo with from Three to Six Mesoblastic Somites (Twfenty-two to Twenty-four Hours' Incubation) a. Whole Mount The darker, more deeply stained part is the embryo. The blastoderm extends beyond the embryo. What is the shape of the area pellucida? What is its compara- tive size? What is the appearance of the area opaca? Is the area vasculosa present? At the head end of the embr\'o the blastoderm is folded back under the embr>'o for a short distance. This fold is called the head-fold. It lifts the head of the embry^o from the yolk. On either side of the middle of the embiyo, extending longitudinally, are two thick- ened plates. In the head region they come almost to- gether, but they diverge or spread out nearly flat toward the tail. These thickened plates are called the neural plates, and the groove between them is called the neural groove. The anterior end of these neural plates wilf form the brain and the remainder will form the spinal card. L^-ing beneath this neural groove is a thick- ened cord of cells, called the notochord. Does the notochord extend the entire length of the neural groove? Beneath the neural plates, or a little to either side of them, are from three to six pairs of more or less cubical thickenings. These are called the mesoblastic somites. How many mesoblastic somites in your embr>'o? The plate of cells extending tailward from the mesoblastic somites is called the segmental plate. With the increase l6 LABORATORY OUTLINES FOR EMBRYOLOGY^ in development of the embryo more mesoblastic somites will be formed from the segmental plates. The posterior region of the embryo, where the neural plates, the seg- mental plates, and the notochord are indistinguishable, is the primitive streak. Are there any blood vessels? Make a drawing of the twenty-four-hour whole mount, showing the things described. Label the parts. Make your drawing large enough so that it will almost fill the page. 2. Embryo with from Ten to Sixteen Mesoblastic Somites (Thirty-three to Thirty-eight Hours' Incubation) a. Whole Mount What is the shape of the area pellucida? What changes have taken place in the area opaca? The irregular, darkly staining parts of the area opaca are blood-islands. This is the beginning of the formation of the vascular area. How does the head-fold differ from the head-fold in the twenty-four-hour chick. The neural folds have united in the median line of the body and formed a tube, the neural tube. How far back is the neural tube closed? The anterior end of the neural tube is considerably enlarged. This enlarged part is the fore- brain. The parts of the fore-brain that project out on either side are the optic vesicles. Posterior to the fore- brain is a second enlargement of the neural tube. It is not so large as the fore-brain. This is the mid-brain. Posterior to the mid-brain are a few enlargements of the neural tube, which constitute the hind-brain. The hind-brain extends to and includes the region of the CHICK, 33 TO 38 hours' incubation 17 third mesoblastic somite. The remainder of the neural tube is the spinal cord or myelon. What is the number of the mesoblastic somites? What change has taken place in the primitive streak? Locate the notochord. The heart lies ventral to the hind-brain. WTiat shape is it? What is the comparative size? The two broad tubes which are connected with the posterior end of the heart are the mtelline veins. A single tube is connected vdth. the heart at the anterior end. This is the ventral aorta. Remember that veins always carr}- blood toward the heart and arteries carry blood away from the heart. Make a drawing of the thirty-six hour whole mount and label all the parts. b. Transverse Sections Sections cut perpendicular to the long axis of the body are transverse sections. It is ver>' difficult to cut sections so that they are exactly perpendicular to a given plane. Many of the sections labeled transverse sections are tipped a little to one side or the other. The sections are cut of uniform thickness and arranged in regular order. Those on most of your slides are fifteen microns thick. A micron is one-thousandth of a millimeter. By counting the number of sections in a series the exact length of the embryo may be calculated, pro\'ided no sections have been lost. The position of any section may be ascer- tained by determining its number in the series. In a transverse section of a chick embryo there are found three kinds of cells, and these different kinds of cells are ar- l8 LABORATORY OUTLINES FOR EMBRYOLOGY ranged in layers that are more or less definite. These layers of cells are called germ layers. The germ layer lying next to the yolk is composed of rather large, rounded cells. This germ layer is the endoderm or hypoblast. The one lying next to the shell and farthest away from the yolk is composed of cuboidal and columnar cells, and is called the ectoderm or epiblast. The one between the ectoderm and the endoderm is composed of irreg- ular cells, and is called mesoderm or mesohlast. All of the organs of the body are formed from these three germ layers. Most of these organs are differentiated from regions of unequal growth with a consequent folding. If this folding is toward the inner part of the body, it is called an invagination; if it is outward from the body, it is called an evagination. The section should be studied with the low power of the microscope unless otherwise indicated. Make out- line drawings with hard pencil and use different colors to represent the germ layers. For the sake of uniformity, color the ectoderm blue, the mesoderm red, and the endoderm green. Do not draw the cells. Indicate on your drawing of the whole mount the location of each section. (i) Through the Fore -brain Showing the Optic Vesicles The head is free from the blastoderm. How has this separation been brought about? Of what germ layers is the blastoderm composed? The mesoderm is in two layers, one lying next to the ectoderm and the other lying next to the endoderm. The layer of ectoderm with CHICK, 33 TO 38 hours' incubatiox 19 the mesoderm which lies next to it forms the somato- pleure, and the endoderm ^\4th the mesoderm lying next to it forms the splanchnopleure. The space or cavity between the splanchnopleure and the somatopleure is the body cavity. If the body cavity is in the embrj'o, it is called the embryonic body cavity or codame. If it is in the blastoderm and not in the embryo, it is called the extra- embryonic body cavity. Is there a coelome in the section in the region of the fore-brain? The ectoderm forms the outer covering of the head. Is it of uniform thick- ness? If not, where is it thickest? The fore-brain is ectodermal in origin. The optic vesicles are evaginations on either side of the fore-brain and are continuous with it. Is the ca\'ity of the fore-brain continuous vdth. the cavities of the optic vesicles? Is there any mesoderm in this section? If so, where? What part is endoderm? It will be observed that the extra-embr\'onic blood vessels are, for the most part, in the mesoderm of the splanchnopleure. Draw the section and label all the parts. Color the germ layers. (2) Through the Middle of the Heart What is the shape of the heart in cross section? Com- parative size? The heart is mesodermal in origin. The inner, thin layer of cells is the endocardium and forms the endothehal lining of the heart. The outer, thicker layer is the myocardium and forms the muscle of the heart. In the splanchnic layer of mesoderm are numerous holes. 20 LABORATORY OUTLINES FOR EMBRYOLOGY These are cross sections of extra-embryonic blood vessels. Dorsal to the heart is a rather large hole, bounded ventrally by a thick wall and dorsally by a thin one. This is a por- tion of the fore-gut, the pharynx. The pharynx is lined with endoderm. In the median line of the body, dorsal to the pharynx, is a circular mass of cells, the notochord. The notochord is endoderm. On each side of the noto- chord and dorsal to the pharynx is a rather large hole. These are dorsal aortce. Why is there no ventral aorta? All blood vessels are formed in mesoderm. What is the neural tube called in this region? The ectoderm of the outside of the body is continuous with the ectoderm of the blastoderm. Is the coelome separated from the extra- embryonic body cavity? Draw the section, label all the parts, and color the germ layers. (3) Through the Region of the Mesoblastic Somites The mesoblastic somites are on either side of the neural tube. They are blocks of mesodermal cells which radiate from a common central point. Connecting each meso- blastic somite with the mesoderm of the somatopleure and the splanchnopleure is a neck of cells. This neck of cells is the intermediate cell mass or nephrotome. The mesodermic layers of the splanchnopleure and the somat- opleure are called the lateral plates. Compare the size of the dorsal aortae here with those in section (i). Draw the section, label all the parts, and color the germ layers. CHICK, 44 TO 48 hours' INCUBATION 21 (4) Through the Primitive Streak Is the notochord present? Are the dorsal aortae present? In the median portion of the body the germ layers cannot be distinguished. Draw the section, label the partSj and color the germ layers. Color black the portion in which the germ layers cannot be distinguished. c. Reconstructions (i) Circulatory System In your sections of the thirty-six-hour chick find the most anterior one which contains the blood vessels. Trace these blood vessels through the remainder of the sections several times. Beginning at the anterior end, sketch in outline all the blood vessels in ever>' third section. iXIake all your sketches on the same scale and keep them in regular order. Think of these sections placed one upon the top of the other in regular order. From your sketches make a diagram of the circulatory system and label all the parts. 3. Embryo with from Twenty-four to Twenty-nine Meso- blastic Somites (Forty-four to Forty-eight Hours' In- cubation) a. Whole Motint It will be observed that a number of striking changes have taken place. These are most noticeable in the head region. In the region of the mid-brain the head has become bent so that the fore-brain and a portion of 22 LABORATORY OUTLINES FOR EMBRYOLOGY the mid-brain form a right angle with the rest of the head. This bend is called the cephalic -flexure. The head is now completely separated from the blastoderm, and the body, which has been continuous with it on the sides, is partly separated from it by the lateral folds, which unite with the head fold. The body has become twisted a short dis- tance back of the region of the heart, so that the head is now lying on its side. Which side? Can you see both optic vesicles? Why? Compare the size of the op tic vesi- cles with that of the fore-brain. What were their relative sizes in the thirty-six-hour chick? The outer part of the optic vesicle has invaginated into the original cavity and has thus formed a cup, the optic cup. The walls of this double cup form the two layers of the retina, which may be seen at this time. What is the comparative thickness of these two layers? The place where the rim of the cup does not appear to be continuous is the choroid fissure. The outside ectoderm in the region of the optic cup has thickened and formed an invagination into the optic cup. This is the lens. It appears as a sphere lying in the optic cup. In the region of the hind-brain is an invagination from the outside ectoderm. This is the auditory vesicle. The heart has elongated more rapidly than the body, consequently it has become twisted upon itself. The vitelline veins are in the lateral folds of the blastoderm. About half way between the vitelline veins and the end of the tail are two blood vessels extending from the embryo into the blastoderm. These are vitelline arteries. They carry the blood from the dorsal aortae to the blastoderm. CHICK, 44 TO 48 hours' INCUBATION 23 Between the hind-brain and the heart in the region of the phar}Tix are two or three pouches or clefts. These are invaginations from the outside ectoderm. Immedi- ately beneath each pouch is an evagination from the phar^Tix. These are the gill-slits (visceral clefts or pouches). Each cleft is bounded on either side by a thicker mass. These masses are the arches. They number from the anterior end. The first arch is the mandibular arch. The second arch is the hyoid arch. The hyomandihidar cleft is between the mandibular arch and the hyoid arch. It is the first \'isceral cleft. The other clefts and arches are numbered in order. Ventral to the mandibular arch and beneath the optic vesicle is a pit or invagination from the outside ectoderm. This marks the location of the future mouth and is called the oral pit. How many mesoblastic somites are there? What changes have taken place in the lateral plates? In the primitive streak? WTiere can you see the notochord? Draw the forty-eight-hour whole mount and label all the parts. b. Transverse Sections The region from which is taken the cross section of which you make a dramng, should always be located on your drawing of the whole mount. ( i) Through the Optic Vesicle showing the Lens, the Choroid Fissure, and the Connection between the Optic Vesicle and the Fore-brain (the Optic Stalk) Because of the cephahc flexure, the plane of this section 24 LABORATORY OUTLINES FOR EMBRYOLOGY passes through the body twice, the fore-brain and the hind-brain. The ventral sides of the two parts He to- gether. Of what germ layer is the brain formed? The optic vesicle? The lens? The outer covering of the body is ectoderm. The part of the body in which the fore-brain is located is enclosed in two membranes, and the part in which the hind-brain is located is almost, if not entirely, enclosed in these two membranes. The membrane next to the body is the amnion and is com- posed of two layers of cells: an inner layer, the ectoderm, and an outer layer, the mesoderm. On the side next to the yolk is the yolk sac, composed of an inner layer of mesodermal cells and an outer layer of endodermal cells. It should be kept in mind that the mesoderm of the yolk sac contains the blood vessels. On the side away from the yolk is the chorion, composed of an inner layer of mesodermal cells and an outer layer of ectodermal cells. What is the shape of the optic vesicle? What is the relative thickness of the layers of the optic vesicle? Is the lens a solid mass of cells? Is it connected to the outside ectoderm or has it become separated? The hind-brain may be distinguished from the fore- brain and the mid-brain on account of its thin roof. What is the shape of the pharynx? The places where the outside ectoderm comes almost in contact with the endoderm of the pharynx are the gill clefts or visceral clefts. The thickened parts between the visceral clefts are the gill arches or visceral arches. In each visceral arch is an aortic arch which carries blood from the ventral aorta to the dorsal aorta. Remember that the ventral CHICK, 44 TO 48 hours' INCUBATION 2$ aorta is always ventral to the gut and that the dorsal aorta is always dorsal to the gut. In this section, how many ventral aortae are there ? How many dorsal aortae ? Dorsal to the dorsal aorta and to either side of the hind- brain are the anterior cardinal veins. The one on the right side is the right anterior cardinal vein and the one on the left side is the left anterior cardinal vein. Where is the notochord? Draw the section, color the different germ layers, and label all the parts. (2) Through the Hind-brain showing the Auditory Vesicles Identify all the parts found in this section that are foimd in the previous sections. Ventral to the fore-brain and between it and the phaivTix is an evagination from the roof of the oral pit, the hypophysis. What is its relation to the brain? Describe the auditory vesicles. Draw the section, color the different germ layers, and label all the parts. (3) Through the Posterior Portion of fee Heart The amnion encloses the embrj'o dorsally, but not ventrally. WTiat part of the central nervous system is here? The mesoblastic somites are no longer thickened blocks of cells, but hare dififerentiated into a somewhat thickened plate of cells, the myotome or muscle-plate, and a mass of cells that are more or less loosely packed together, the sclerotome. What is the size and shape of the gut in this section? Notice the thickened walls of 26 LABORATORY OUTLINES FOR EMBRYOLOGY the coelome, or body cavity. How many dorsal aortae are here? Is the ventral aorta present in this section? Why? Between the body cavity and the outside of the body on either side is a blood vessel. If this blood vessel be traced through the different sections, it will be seen that it connects the cardinal veins with the heart. It is the duct of Cuvier. It is formed by the union of the anterior and posterior cardinal veins and empties into the heart near the place where the vitel- line veins join the heart. Identify the myocardium and the endocardium. Draw the section, color the different germ layers, and label all the parts. (4) Through the Embryo about Half Way between the Heart and the Posterior End Note the beginning of the folding up of the somato- pleure to form the amnion. The point on each side where the lateral fold delimits the embryonic from the extra-embryonic area is the lateral limiting sulcus. What is the character of the mesoblastic somites? How have the myotome and sclerotome been formed? On the dorsal surface of the nephrotome is a thick cord of cells with a small hole in it. This is the Wolffian duct or mesonephric duct. How many dorsal aortae ara there? Are the cardi- nal veins found in this section? If they are present, they are called the posterior cardinal veins. Draw the section, color the different germ layers, and label all the parts. CHICK, 68 TO 72 hours' incubation 27 c. Reconstructions (i) The Circulatory System In your sections trace the circulatory system through several times. Make outline drawings of the blood vessels in about every third section. Make all your out- line drawings on the same scale, keeping the relative position and shape that are seen in the sections. Keep your drawings in consecutive order. From your drawings make a diagram of the circulatory system of the forty-eight-hour chick and label all the parts. What changes have taken place in the circulation between the thirty-six-hour chicken and the forty- eight-hour chicken? (2) The Central Nervous System Trace the central nervous system through several times. IMake outline drawings of every third section of it. Think of these sections as having a definite thickness and placed one upon the other in regular order. Make a diagrammatic drawing of the central nervous system and label all the parts. 4. Embryo with from Thirty-five to Thirty-seven Meso- blastic Somites (Sixty-eight to Seventy-two Hours* Incubation) a. Whole Moimt It will be observed that the whole embrj^o is now" lying on its side. There is another bend in the head region. This bend is in the region of the hind-brain and is called 28 LABORATORY OUTLINES FOR EMBRYOLOGY the nuchal or cervical flexure. Now the region of the hind-brain is the most anterior part of the embryo. The lateral folds have been completed and the tail fold is well formed. In the tail region the digestive tract has begun to fold off from the yolk sac. The posterior part of the digestive tract is called the hind-gut. Ante- rior to the tail-fold on the ventral side of the hind- gut is a bladder-like evagination. This is the allantois. The amnion has completely closed, dorsally. The heart is now within the body. Can you trace the twists of the heart? What changes have taken place in the eye? The ear? How many visceral clefts are there? The fore-brain is now composed of two parts: an anterior part composed of two lobes, the telencephalon, and a part immediately back of this, the thalamencephalon, some- times called the diencephalon. The telencephalon is the rudiment of the cerebral hemispheres. Toward the ventral surface of the telencephalon and anterior to the eye is an invagination from the outside ectoderm, the olfactory pit. There is a short diverticulum in the roof of the thala- mencephalon. This is the epiphysis. The mid-brain forms the apex of the cephalic flexure. The mid-brain is the mesencephalon. Between the mid-brain and the hind-brain, the central nervous system is considerably narrowed. This narrow part is the isthmus. The hind- brain is composed of two parts, the metencephalon and the myelencephalon. The metencephalon is the most anterior part of the hind-brain and is the rudiment of the cerebellum. The myelencephalon has a thin roof and sides. It is the rudiment of the medulla oblongata. CHICK, 68 TO 72 hours' incubation 29 Draw the seventy-two-hour whole mount and label all the parts. b. Transverse Sections Study your sections and on your drawing of the whole mount indicate the angle at which they have been cut. (i) Through the Auditory Vesicle This section passes through the body t^^^ce. Why? Are the two parts of the body separate or continuous? What portions of the central nervous system are shown in each part? What blood vessels are seen in this section? If you cannot tell by looking at only the one section, trace them through and compare ^^nth the blood vessels in your sections of the forty-eight-hour chick. Between the floor of the hind-brain and auditory vesicle may be seen the gangUon complex of the seventh and eighth cranial nerves, the acustico-Jacialis ganglion. Above the third aortic arch and ventral to the auditory vesicle is the ganglion of the ninth cranial nerve, the glosso-pharyngeal ganglion. Draw the section, color the different germ layers, and label all the parts. (2) Through the Optic Vesicle Your section should be selected so that it will show, if possible, the choroid fissure, the lens, and the optic stalk. What part of the fore-brain is in yoiu- section? A part of the hind-brain also may be in the section. WTiat is the relative position of the different parts of the brain? 30 LABORATORY OUTLINES FOR EMBRYOLOGY What is the shape of the lens? Of how many layers of cells is it composed? Identify all the blood vessels. Are the Wolffian ducts present? If present, where are they? What has become of the mesoblastic somites? The fore-gut may have two diverticula, one on either side of the ventral part. These are the lung-buds. Draw the section, color the different germ layers, and label all the parts. (3) Through the Olfactory Pits Where are the olfactory pits with reference to the fore- brain? Does this section pass through the mid-brain? Identify all the blood vessels in the section. The rather elongated ventral evagination from the fore-gut is the first liver diverticulum. Find the Wolffian ducts. Near the Wolffian ducts are one or more rather thickened tubules. These are the beginnings of the Wolffian bodies. It will be seen that the gut and the tissue imme- diately surrounding it are connected to the body dor- sally by a neck of tissue. This neck of tissue is the dorsal mesentery. There is also a short neck of tissue ventral to the gut. This is the ventral mesentery. The thicken- ings of the body wall to the side of the posterior part of the body cavity are the fore-limb buds. Draw the section, color the different gerfit layers, and label all the parts. (4) Through the Allantois Where it is Connected with the Hind-gut The allantois is a bladder-like evagination from the ventral side of the posterior part of the hind-gut. What CHiOK, 68 TO 72 hours' incubation 31 is its shape in the section? Is the body closed ventrally? What is the shape of the body cavity? Locate the Wolf- fian ducts. Are the Wolffian bodies in this section? The thickening of the body wall to the sides of the body cavity are the hind-limb huds. Does the amnion entirely enclose the body? Draw the section, color the different germ layers, and label all the parts. c. Reconstructions (i) The Alimentary Tract and Its Appendages Beginning with the most anterior part, trace the ali- mentary^ tract through all the sections. It will be seen that from the most anterior part to the region of the vitelline veins it is an irregular tube. This part of it is the fore-gut. From the fore-gut posteriorly for about a third or a fourth of the length of the embryo the aUmen- tar>' tract is continuous with the yolk sac. In the poste- rior part it again forms a tube, the hind-gut. The alimentary tract continues to fold off from the yolk sac until the fore-gut and the hind-gut meet. They meet in the posterior part of the duodenum. The most anterior part of the fore-gut, that is, the portion beneath the fore-brain, is comparatively small. This is the hypoph- ysis. Suddenly it becomes very large and irregular. The lateral irregularities are the visceral pouches and clefts. How many? Ventral to the second visceral pouch is a long, narrow evagination, the thyroid gland. The pharynx becomes flattened laterally to form the trachea, and then the lung-buds are given off. Poste- 32 LABORATORY OUTLINES FOR EMBRYOLOGY rior to the lung-buds the gut narrows into the short oesophagus. Soon it enlarges somewhat to form the stomach. The ventral evagination of the duodenum is the liver. In the hind-gut the ventral bladder-like evagination, as was mentioned before, is the allantois. From your study of these sections, reconstruct the ali- mentary tract and its appendages and make a drawing of it as an opaque object, lateral view. THE PIG EMBRYO I. Ten-millimeter Embryo a. Whole Embryo Remove all the membranes from a ten-millimeter pig embryo. Examine the external form with the dissecting microscope or the hand lens. It will be noticed that the head is very large in comparison with the body. It forms nearly a right angle with the remainder of the body. This marks the location of the hind-brain. Anterior to the hind-brain is an enlarged part which makes a rounded angle. This marks the position of the mid-brain. The fore-brain is now composed of two rounded lobes, the rudiments of the cerebral hemispheres. In the angle ventral to the fore-brain and the mid-brain is the lens of the eye surrounded by the edges of the optic cup. Extending from the eye ventrally is a depression or groove, the lachrymal groove. The lachrymal groove leads to an invagination forming a cup-like pit ventral to the anterior part of the fore-brain. This invagination PIG EMBRYO, TEN-MILLIMETER 33 is the olfactory pit. Caudal to the lachr>^mal groove and dorsal to the olfactory pit is a thickened part, the maxil- lary process which will form the greater part of the upper jaw. Caudal to this thickening is a second one, the mandibular process, which will form the lower jaw. The first gill cleft remains as a groove caudad to the mandibu- lar process. This marks the position of the future ex- ternal auditory meatus. The second, third and fourth gill clefts have disappeared and their remains are marked by a triangular depression, the apex of which is at the ventral terminus of the first gill cleft. This depression is the cervical sinus. Note that the length of the dorsal side of the embrj^o is three or more times the length of the ventral side. On the dorsal side from the hind-brain terminating in the slender tail are a number of segments, the muscular segments. On the ventral side of the embryo is the large umbilical cord. Its connection with the em- bryo occupies about one-third of the ventral part of the body or almost all of the ventral surface of the abdominal region proper. Anterior to the umbilical cord the cardiac region protrudes ventrally. Between the cardiac region and the muscular segments is a large evagination, the fore-limb bud. Between the posterior connection of the umbilical cord to the body and the origin of the tail is another smaller evagination, the hind-limb bud. Extend- ing from the fore-limb bud to the hind-limb bud along the curvature of the body is the milk ridge. Draw the whole embryo to scale and label all the parts. 34 LABORATORY OUTLINES FOR EMBRYOLOGY b. Transverse Sections The transverse sections should be parallel to the length of the hind-brain. Indicate on your drawing of the whole embryo the region from which each section is taken. (i) Through the Anterior Part of the Otocyst This section passes through the body twice. The hind-brain has a very thin dorsal wall. Its lateral walls have several irregular folds, the neuromeres. The fore- brain appears as an oval section of the central nervous system. On either side of the body near the hind-brain are the otocysts. The rather sharp evagination of the otocyst extending toward the hind-brain is the endolym- phatic duct. Ventral to the otocyst and between it and the hind-brain is the acustico-facialis ganglion. To the side of the hind-brain and almost between it and the fore-brain is the large trigeminal ganglion. Dorsal to the otocyst and to the side of the hind-brain is the vagus ganglion. Dorsal to the vagus ganglion may be seen fibers of the spinal accessory nerve. Draw the section, color the germ-layers, and label all the parts. (2) Through the Choroid Fissure and the Optic Stalk This section passes through the fore-brain and the spinal cord. The spinal cord has differentiated into two distinct zones, the dorsal zone and the ventral zone. From either side of the spinal cord may be seen the roots of the spinal nerves. The notochord is small compared with the notochord of the chicken. Identify the jugular PIG EMBRYO, TEN-MILLIMETER 35 vein on either side of the body ventral to the spinal cord. Near the jugular vein is the united vagus and spinal accessory nerve. Ventral to this nerve and also near the jugular \'ein is the petrosal ganglion of the ninth nerve. Identify the gill clefts and gill arches, the carotid artery, the pharynx, the optic stalk, the two layers of the retina, the choroid fissure, the lens, the cerebral hemispheres. Ventral to the first gill cleft is the maxillary nerve. Draw the section, color the germ layers, and label all the parts. (3) Through the Middle of the Heart and the Fore-limb Buds The description of the spinal cord as given in section (2) will apply here also. At the origin of the limb bud is a nerve plexus, the brachial plexus. Dorsal to the brachial plexus is a blood vessel, the subclavian vein. Ventral to the notochord and on either side of the median line of the body is the dorsal aorta. Between the two dorsal aortae and a little ventral to them is the oesophagus. Ventral to the oesophagus is the trachea. Ventral to the limb buds and on either side of the trachea is a large irregular blood vessel, the duct of Cuvier. The heart is now divided into four chambers, the two auricles and the two ventricles. The walls of the ventricles have become thickened and now have some of the characteristics of heart tissue. The tissue between the two ventricles is the ventricular septum. The triangular pieces of tissue extending from the dorsal wall of each ventricle dowTi into the cavity of the ventricle are the auricular-ventricu- lar valves. The ca\aties of the auricles are larger than 36 LABORATORY OUTLINES FOR EMBRYOLOGY the cavities of the ventricles but the walls are very much thinner. The two auricles are separated dorsally by a thin membrane, the septum spurium. They are sepa- rated ventrally by a thicker membrane, the continuation of the ventricular septum. Draw the section, color the germ layers, and label all the parts. (4) Through the Body about Half Way between the Fore-limb Buds and the Hind-limb Buds This section passes through the umbilical cord. The description of the spinal cord given in section (2) will apply here. The dorsal aorta is a single vessel in this region. On either side of the dorsal aorta is a large body filled with holes. These bodies are the Wolffian bodies. The part of the digestive tract in this region is the stomach. It is connected to the body dorsally by a neck of mesoderm, the major omentum. The mesoderm con- tinuing from the stomach ventrally is the minor omentum. Surrounding the stomach laterally and ventrally are four large lobes of tissue filled with holes. These masses of tissue are the lobes of the liver. The large blood vessel in the right dorsal lobe is the inferior vena cava. The large blood vessels in the ventral lobes are the um- bilical veins. In the tissue between the liver lobes is a hole surrounded by a thickened wall, the gall-bladder. Identify the umbilical arteries in the umbilical cord. On the ventro-median surface of the Wolffian body, near the dorsal end of the major omentum, is a ridge, the genital ridge. PREGNANT UTERUS 37 Draw the section, color the germ layers and label all the parts. 2. The Pregnant Uterus Uteri containing embryos three or four inches in length may be obtained from any large slaughter house. The whole uterus with the ovaries should be secured. If they are preserved and hardened for a few days in ten per cent, formalin, then transferred to three or four per cent, formalin, and finally soaked in water three or four days before using, they will be well preserved and most of the disagreeableness of the formalin preservatives will be removed. It is well to change the water some two or three times. Examine the uterus and note that it is composed of two rather large tubes united at one end and free at the other. These are called the horns of the uterus. The horns are united at the vagina. Along the inner edge of each horn is a broad, tough, flat membrane which causes the outer edge to form a ruffle. This membrane is the broad ligament. The location of the embryos in the uterus is indicated by the enlargements. Note the many branched blood vessels beneath the surface of these enlargements. Trace one horn of the uterus to the free end. It will be seen that the horn suddenly' narrows down into a tube that is about the size of a large knitting needle. This tube is the Fallopian tube or oviduct. The Fallopian tube ends distally in a thin membrane which surrounds the ovary, with the exception of an opening into the body cavity. This terminal opening is the ostium tubx ab- 38 LABORATORY OUTLINES FOR EMBRYOLOGY dommale. What is the size of the ovary? Shape? The large, colored irregularities of the ovary are the recent corpora lutea. How many in each ovary? How does the number compare with the number of embryos in the uterus? The smaller, rounded spots that re- semble blisters are Graafian follicles. Open one of the Graafian follicles. What is the nature of the contents? With a pair of scissors or scalpel remove one of the enlargements by cutting mid-way between two of them. Cut through the broad ligament. Open this part of the uterus by cutting longitudinally the side opposite the broad ligament. This cut should pass through the walls of the uterus and the outer embryonic covering, the chorion. In the pig, the chorion is composed of the chorion proper and the wall of the allantois. From one side carefully separate the chorion from the walls of the uterus. Note that the inner layer of the uterine wall is in folds which extend around the embryo. Also note the blood vessels in this layer. What is the position of the chorion with reference to these folds? Carefully sepa- rate the chorion from the amnion. The amnion is semi- transparent and is a much thinner membrane than the chorion. Note the blood vessels in the chorion. (The blood vessels are in the allantoic wall of the chorion.) Compare them with the blood vessels of the lining of the uterus. Also note the very small blood vessels of the amnion. To the ventral side of the embryo is the um- bilical cord, which connects the embryo to the chorion. Draw the embryo in position, showing the blood vessels DISSECTION OF THE PIG EMBRYO 39 and connection of the embryo to the chorion. Label all the parts. Carefully remove the entire chorion from the uterus. It will be seen that the only connection of the embryo to the uterus is the contact of the chorion and the mucous lining of the uterus. Open the amnion on the dorsal side of the embryo. It will be seen that it is not connected with the embryo except at the distal end of the umbilical cord. How many blood vessels in the umbilical cord? The blood vessels may be distinguished from the re- mainder of the tissue in the umbilical cord by their dark color, due to the blood in them. The colorless tube in the umbilicus is the allantois. 3. The Dissection of the Embryo a. The Abdomen Cut aw^ay the amnion and the chorion except for a small part at the end of the umbilicus. Open the em- bryo in the mid-ventral line, being careful to separate the tissue from the umbilicus. Do not break any of the blood vessels or the allantois. Pin back the body wall. The large, reddish-brown mass exposed is the liver. Separate the blood vessels in the umbilicus and trace them into the body. The one going to the liver is the umbilical vein. The other two are the umbilical arteries. Trace the allantois toward the posterior end. The en- largement of the allantois in the pelvic region is the uri- nary bladder. A tube from either side enters the bladder on the dorsal surface near the posterior end. These are the ureters. Separate the tube leading from the bladder 40 LABORATORY OUTLINES FOR EMBRYOLOGY to the outside of the body. This is the urethra. With- out removing any of the liver, examine it. Of how many lobes it is composed? Size? Position? Dorsal to the liver and a little posterior to it is the much coiled in- testine. Dorsal to the bladder and ventral to the ureters are two fine tubes, one on either side, which unite dorsal to the posterior end of the bladder. These tubes are the Fallopian tubes in the female or the vas deferens in the male. The posterior part of the Fallopian tubes forms the horns of the uterus, which unite near the vagina. The point of union of the vas deferens forms the sinus pocularis, or male uterus. Trace the sex ducts until they open to the exterior- Near the anterior end of the sex ducts and a little ventral to them are the sex glands, the ovaries if female, or the testes if male. Dorsal to the sex glands and toward the median line of the body are the remains of the Wolffian bodies. By lifting the intestine and the posterior part of the liver, a part of the comparatively large kidneys may be seen. Trace the ureters to the kidneys. In the median line of the body, extending between the sex ducts and posteriorly dorsal to the urethra, is the posterior end of the intestine, the descending colon and the rectum. Draw the dissection and label all the parts. Trace the umbilical vein through the liver by carefully dissecting away a small part of the liver at a time. Im- mediately dorsal to the anterior part of the liver is the stomach. What is its shape? Position? The small bladder found in the liver is the gall bladder. The duct leading from the gall bladder is the cystic duct. This DISSECTION OF THE PIG EMBRYO 4 1 unites with another small duct, the hepatic duct, to form the common bile duct. The common bile duct empties into the intestine a short distance posterior to the py- loric end of the stomach. L^dng along the greater curva- ture of the stomach is a dark-colored body, the spleen. How is it held in position? Dorsal to the stomach is a whitish body, the pancreas. What is its shape? Posi- tion? A duct leads from the pancreas to the intestine. This is the pancreatic duct, or the diict of Wirsung. It empties into the intestine near the place where the com- mon bile duct empties into the intestine. How is the intestine held in position? The connective tissue that holds the intestine in position is the mesentery. Care- fully remove the mesentery and straighten out the in- testine. Is it a continuous tube? How long is it? What marks the transition from the large to the small intestine? Is there a difference in size between the large and the small intestine? In length? Trace the umbilical arteries to their origin. They are branches of the dorsal aarta. A short distance from the aorta the umbilical arteries branch, one part going to the umbilicus and the other going to the hind leg. The one going to the hind leg is the iliac artery. A short distance posterior to the origin of the umbilical arteries the aorta divides into two parts. These are the caudal aortce. Trace the aorta to the diaphragm. Note the branches given off to the kidneys, renal arteries; to the mesentery, superior mesenteric artery; to the liver, hepatic artery; and to the stomach, the gastric artery. Dorsal to the iliac arteries are the iliac veins. They 42 LABORATORY OUTLINES FOR EMBRYOLOGY unite to form the ascending vena cava. From the kid- neys, ventral to the renal arteries, the ascending vena cava receives the renal veins. Trace the ascending vena cava to the diaphragm. How does the blood from the umbilical vein get into it? Where does the blood from the intestine go? Draw a diagram of the circulation thus far worked out and label all the parts. h. The Thorax What blood vessels pass through the diaphragm? The oesophagus extends from the stomach through the diaphragm into the thorax. Separate the diaphragm from the body wall. The masses of tissue occupying the greater part of the thoracic cavity are the lungs. How many lobes? Size? Shape? Position? What is the position of the heart? Size? Shape? The heart is enclosed in a thin connective tissue sac, the pericardium. The point of the heart is called the apex and the other end is called the base. The firm, muscular part of the heart composes the ventricles and the darker colored, softer portion at the base composes the auricles. Both the auricles and ventricles are called right and left, according to their position. Trace the aorta to the heart. Where does it enter the heart? How many arches has the aorta now? The artery lead- ing from the ventricle to the lungs is the pulmonary artery. Which ventricle? What is the relation of the pulmonary artery to the lungs? From the anterior part of the arch of the aorta arises a vessel which carries the DISSECTION OF THE PIG EMBRYO 43 blood toward the head. This vessel is the innominate artery. Branches from the innominate arter}' are given off laterally, going to each fore-limb, the right and left subclavian arteries. Do you find the carotid arteries leading from the innominate arter}^ to either side of the head? Trace the inferior vena cava vein to the heart. With what part of the heart does it connect? The superior vena cava and the inferior vena cava empty into the heart near the same place. The blood from the ante- rior part of the body is collected in the superior vena cava. Trace it and its branches to the neck and fore-legs. Do you find the pulmonary veins? The pulmonary veins carry the blood from the lungs to the heart. What part of the heart? Open the heart. Describe the valves separating the auricles from the ventricles. The two ventricles are separated by a muscular wall, the ventric- ular septum. The two auricles are not separated. The opening between the two auricles is the foramen ovale. Is there any trace of the formation of the auricular septum ? Draw a diagram of the circulatory system in the thorax as you have found it in your dissection. Label all the parts. Trace the lungs to the mouth. Trace the oesophagus to the mouth. What is the relation of the oesophagus to the trachea and larynx? INDEX Abdomen of pig, dissection of, 39 Achromatin, i Acustico-facialis ganglion, 29, 34 Air-chamber, 12, 13 Alimentary tract and its append- ages, reconstruction of in chick of sixty-eight to seventy-two hours' incu- bation, 31 Allantois, 28, 30, 32, 38 Amnion, 24, 25, 26, 38, 39 Amphibia, 8 Amphioxus, 8 Anaphases, 2, 7 Animal pole, 10 Anterior cardinal vein, 25, 26 Aorta, caudal, 41 dorsal, 20, 21, 24, 35, 41 ventral, 17, 20, 24 Aortic arch, 24 Archenteron, 11 Area opaca, 14, 15, 16 pellucida, 5, 14, 15, 16 vasculosa, 14, 15 Artery, carotid, 35, 43 gastric, 41 hepatic, 41 iliac, 41 innominate, 43 pulmonary, 42 renal, 41 subclavian, 43 superior mesenteric, 41 umbilical, 36, 39, 41 vitelline, 14, 22 Arthropoda, 9 Ascaris, 6, 7 Auditory vesicle, 22, 25, 29 Auricles, 35, 42 Auricular septum, 43 -ventricular valves, 35 Blastoderm, 12, 14, 15, 18, 20, 22 Blastopore, 11 Blastula, 11 Blood islands, 16 Body cavity, embryonic, 19, 26 extra-embryonic, 19 Brachial plexus, 35 Brain, 15 fore-brain, 16, 21, 28, 32, 34 hind-brain, 17, 25, 28, 32, 34 mid-brain, 16, 21, 32 Broad ligament, 37 Cardiac region, 33 Cardinal veins, anterior, 25 posterior, 25 Carotid artery, 35 Caudal aortae, 41 Cell, division, i parts of, I in astroid stage, 2 in diastroid stage, 2 in di-spireme, 3 in metaphase, 2 in resting stage, i in spireme stage, i Cells, stroma, 5 follicular, 5 Cell-wall, I 45 46 INDEX Centrosome, i, 2 Cephalic flexure, 22, 23 Cerebellum, 28 Cerebral hemispheres, 28, 32, 35 Cervical flexure, 28 sinus, 33 Chalazae, 12 Chick embryo, 15, 16 Choroid fissure, 22, 29, 34, 35 Chorion, 24, 38 Chromatin, i, 3, 6 Chromosomes, 2, 6 Circulatory system, reconstruction of in chick of thirty-three to thirty-eight hours' in- cubation, 21 of forty-four hours' incuba- tion, 27 Cleavage, kinds of, 8 stages of, ID Coelome, 19, 20, 26 Colon, descending, 40 Common bile duct, 41 Corona radiata, 5 Corpora lutea, 38 Cyclostomata, 8 Cytoplasm, i, 3, 6, 7, 9, 12 Cystic duct, 40 Daughter cells, 3 Descending colon, 40 Deutoplasm, 4 Diaphragm, 41, 42 Diaster, 3 Diencephalon, 28 Discoidal cleavage, 9 Discus proligerus, 5 Dissection of pig embryo, 39 Dorsal aorta, 20, 21, 24, 35, 41 mesentery, 30 zone of spinal cord, 34 Duodenum, 32 Duct of Cuvier, 26, 35 of Wirsung, 41 Dyad, 6 Echinodermata, 8 Ectoderm, 18, 10. 00 Egg, cleavage of, 8 fertilization of, 7 formation of, 4 hard-boiled, 13 hen's, 12 incubated, 14 maturation of, 6 parts of, 4 raw, 12 Embryo of chick, fixed and stained, 15 transverse sections of, 17, 23, 29 live, 14 whole mount, 15, 16, 21, 27 of pig, dissection of, 39 pregnant uterus, 37 ten millimeter, 32 transverse sections, 34 whole embryo, 32 Embryonic body cavity, 19 Endocardium, 19, 26 Endoderm, 18, 19, 20 Endolymphatic duct, 34 Epiblast, 18 Epiphysis, 28 Equal cleavage, 9 Evagination, 18 External auditory meatus, ^:i Extra-embryonic body cavity, 19, 20 Eye, lens of, 22, 23, 30, 32, 35 Fallopian tube, 37, 40 Fertilization, 3 INDEX 47 Follicular cavity, 5 cells, 4, 5 fluid, 5 Foramen ovale, 43 Fore-brain, 16, 19, 21, 28, 32, 34 -gut, 30 -limb budo.ib, 33, 36 Frog's eggs, 10 Gall-bladder, 40 Ganglion, acustico-facialis, 29, 34 glosso-pharyngeal, 29 petrosal, 35 trigeminal, 34 vagus, 34 Gastric artery, 41 Gastrula, 11 Gastrulation, 11 Genital ridge, 36 Germinal epithelivun, 4 spot, 4, 9 vesicle, 4, 9 Germ layers, 18 Gill arches, 24, 35 clefts, 23, 24, 33, 35 slits, 23 Glosso-pharyngeal ganglion, 29 Graafian follicle, 4, 6, 38 young, 4 ripe, 5 Growth period, 6 Hard-boiled egg, 13 Head cap, 3 -fold, 15 Heart, 14, 17, 19, 25, 26, 28, 42 Hepatic artery, 41 duct, 41 Hind-brain, 17, 25, 28, 32, 34 -gut, 28, 30 -limb buds, 31, 33, 36 Holoblastic cleavage, 8, 9 Horns of uterus, 37 Hyoid arch, 23 Hyomandibular cleft, 23 Hypoblast, 18 Hypophysis, 25, 31 Iliac artery, 41 veins, 41 Incubated egg, 14 Inferior vena cava, 36 Innominate artery, 43 Intermediate cell mass, 20 Intestine, 40, 41 Invagination, 18 Isthmus, 28 Jugular vein, 34 Karyokinesis, 3 Kidneys, 40 Lachrymal groove, 32 Laiynx, 43 Lateral folds, 22 plates, 20, 22, 23 limiting sulcus, 26 Lens of eye, 22, 23, 30, 32, 35 Liver, 32, 36, 39 diverticulum, 30 Lung buds, 30 Lungs, 43 Major omentum, 36 Mammalia, 8 Mandibular arch, 23 process, 33 Maturation, 6 Matured ovum, 7 MaxiUarj'- nerve, 35 process, 33 Medulla oblongata, 28 Meroblastic cleavage, 9 Mesencephalon, 28 48 INDEX Mesentery, 41 dorsal, 30 ventral, 30 Mesoblast, 18 Mesoblastic somites, 15, 20 Mesoderm, 18, 20 Mesonephric duct, 26 Metaphase, 2, 6, 7 Metencephalon, 28 Mid-brain, 16, 17, 21, 32 -piece, 3 Milk ridge, 33 Minor omentum, 36 Mitosis, 3 Monad, 7 Muscle-plate, 25 Muscular segment, 33 Myelencephalon, 28 Myelon, 17 Myocardium, 19, 26 Myotome, 25 Nephrotome, 20, 26 Nerve, maxillary, 35 ninth, 35 spinal accessory, 34, 35 vagus, 35 Neural groove, 15 plates, 15 tube, 16, 17 Neuromores, 34 Ninth nerve, 35 Notochord, 15, 17, 20, 21, 23, 34 Nuchal flexure, 28 Nuclear membrane, i Nucleolus, I Nucleus, I, 2, 8, 9 of Pander, 13 (Esophagus, 32, 35, 43 Olfactory pit, 28, 33 Oocyte, 7 Optic cup, 22, 32 stalk, 23, 29, 34, 35 vesicles, 16, 19, 22, 23, 29 Oral pit, 23 Ostium tubae abdominale, 37 Otocyst, 34 Ovaries, 4, 38, 40 Ovary of cat, 4 Oviduct, 37 Ovum, formation of, 4 Pancreas, 41 Pancreatic duct, 41 Pericardium, 42 Peripheral cleavage, 9 Petrosal ganglion, 35 Pharynx, 20, 25, 35 Pig embryo, ten millimeter, trans- verse sections, 34 whole, 32 dissection of, 39 Polar body, 7 Posterior cardinal vein, 25, 26 Pregnant uterus, 39 Primitive streak, 16, 17, 21, 23 Pronucleus, 7, 8 Prophases, 2 Pulmonary arteries, 42 veins, 43 Raw egg, 12 Reconstructions of circulatory sys- tem of chick of thirty- three to thirty-six hours' incubation, 21 of circulatory system of chick of forty-four to forty- eight hours' incubation, 27 of central nervous system of chick of forty-four to forty-eight hours' incuba- tion, 27 INDEX 49 Reconstructions of alimentary tract and its appendages in chick of sixty-eight to seventy-two hours' incu- bation, 31 Rectum, 40 Renal arteries, 41 veins, 42 Retina, 22, 35 Sclerotome, 25 Sections of chick embryo, trans- verse, thirty-three to thirty-six hours' incuba- tion, 17 forty-four to forty-eight hours' incubation, 23 sixty-eight to seventy-two hours' incubation, 29 of ten millimeter pig, trans- verse, 34 Segmental plate, 16 Segmentation, 8 cavity, 11 Septum spurium, 36 Shell membrane, 12 Sinus pocularis, 40 Somatopleure, 19, 26 Somites, 15, 20 Spermatozoan, 8 parts of, 3 Spinal accessory nerve, 34, 35 cord, 15, 17, 34 dorsal zone, 34 ventral zone, 34 Spindle fibers, 2, 7 Spireme, i, 2 Splanchnopleure, 19 Spleen, 41 Starfish egg, 9 Stomach, 36 Stratum granulosum, 5 Stroma, 5 Subclavian artery, 43 vein, 35 Superior mesenteric artery, 41 vena cava, 43 Tail, 3, 15. 33 Telencephalon, 28 Telophases, 3 Testes, 40 Tetrad, 6 ThaJamencephalon, 28 Theca folliculi, 5 Thorax of pig, dissection of, 42 Thyroid gland, 31 Trachea, 3ii 35 Transverse sections of chick, thirty-three to thirty-six hours' incubation, 17 forty-four to forty-eight hours' incubation, 23 sixty-eight to seventy-two hours' incubation, 29 of ten millimeter pig, 34 Trigeminal ganglion, 34 Umbilical artery, 36, 39 cord, 33, 36, 38 vein, 36, 39, 40 Unequal cleavage, 10 Urethra, 40 Ureter, 39 Uterus, horns of, 37 Urinary bladder, 39 Vagina, 37, 40 Vagus ganglion, 34 nerv'e, 35 Vascular area, 16 Vas deferens, 40 V^etative pole, 10 50 INDEX Veins, anterior cardinal, 25, 26 posterior cardinal, 25, 26 iliac, 41 inferior vena cava, 36, 42 jugular, 34 pulmonary, 43 renal, 42 superior vena cava, 43 subclavian, 35 umbilical, 36, 39, 40, 42 vitelline, 14 Ventral aorta, 17, 20, 24 mesentery, 30 zone of spinal cord, 35 Ventricular septum, 35, 43 Ventricles, 35, 42 Visceral arches, 24 clefts, 23 pouches, 23 Vitelline arteries, 14, 22 membrane, 4, 5, 12, 13 veins, 14, 17 White yolk, 13 Whole embryo ten millimeter pig, 32 Whole mount of chick embryo, twenty-two to twenty- four hours' incubation, 15 thirty-three to thirty-six hours' incubation, 16 forty-four to forty-eight hours' incubation, 21 sixty-eight to seventy-two hours' incubation, 27 Wolffian body, 30, 36, 40 duct, 26, 30 Yellow yolk, 13 Yolk, 4, 8, 12, 13, 14, 15, i! sac, 24 Zona pellucida, 5 ANATOMY REFERENCE LIBRARY 'his Bcx)k must not be taken fron, he Oept ^* A -.^4.-^-^, _ PLEASE DO NOT REMOVE CARDS OR SUPS FROM THIS POCKET UNIVERSITY OF TORONTO UBRARY ■^"■^^^ H3 Hannan,- Mary Theresa La"boratory outlines for emiaryology BioMed.