শিক্ষামূলক নোট: এই পৃষ্ঠা একাডেমিক জীববিজ্ঞান শেখা ও পরীক্ষার প্রস্তুতির সহায়ক।
External Morphology and Dissection
Syllabus Map
Major dissection
- Circulatory system — earthworm, prawn
- Nervous system — cockroach, grasshopper, prawn, Pila, Lamellidens
- Reproductive system — earthworm, cockroach, grasshopper, prawn
Minor dissection
- Digestive system — prawn, Pila, Lamellidens
- Nervous system — cockroach, grasshopper, prawn
Major/minor overlap syllabus অনুযায়ী preserve করা হয়েছে; examination instruction অনুযায়ী display depth আলাদা হতে পারে।
General Dissection Rules
- Specimen আগে external orientation নিশ্চিত করো।
- Pinning এমনভাবে করবে যাতে target organ-system stretch বা tear না হয়।
- Cut line shallow রাখবে; internal organs blind-cut করবে না।
- Dissection needle দিয়ে connective tissue separate করবে—organ টেনে ছিঁড়বে না।
- Display-তে unnecessary tissue remove না করে target structure expose করবে।
- Wet specimen শুকাতে দেবে না।
- Drawing-এর orientation dissection tray-এর orientation-এর সঙ্গে consistent হবে।
A. External Morphology
Earthworm
Label: prostomium, mouth, segments, clitellum, dorsal pores, setae, genital pores, anus.
Cockroach
Label: head, antennae, compound eyes, pronotum, fore/hind wings, three leg pairs, abdominal segments, cerci; male/female terminal differences.
Prawn
Label: rostrum, carapace, stalked eyes, antennules, antennae, pereiopods, abdominal segments, pleopods, telson, uropods.
Pila
Label: shell apex, spire, sutures, body whorl, aperture, operculum; living specimen-এ head, tentacles, foot.
Lamellidens
Label: valves, umbo, hinge line, growth lines; opened specimen-এ mantle, gills, foot, siphonal region.
B. Major Dissections
1. Earthworm — Circulatory System
Aim
Dorsal vessel, ventral vessel, hearts/aortic arches এবং প্রধান vascular connections expose করা।
Orientation
Specimen dorsal side upward; anterior end identify করো।
Display sequence
- Shallow mid-dorsal incision।
- Body wall lateral pinning।
- Septa carefully cut where needed।
- Alimentary canal-এর dorsal surface বরাবর dorsal blood vessel trace।
- Anterior region-এ paired hearts/aortic arches identify।
- Gut gently displace করে ventral vessel দেখানো।
- Nephridia/reproductive organs unnecessarily damage করবে না।
Final labels
Dorsal vessel, ventral vessel, lateral hearts/aortic arches, intestinal vessels.
Common error
Dorsal vessel-কে gut wall-এর pigmented line ধরে নেওয়া; vessel continuity verify করবে।
2. Prawn — Circulatory System
Aim
Dorsal heart and major arterial origins demonstrate করা।
Display sequence
- Dorsal carapace carefully remove।
- Pericardial region expose।
- Dorsal polygonal/triangular heart identify।
- Ostia observe where possible।
- Anterior and posterior arterial branches trace without tearing hepatopancreas/gonad unnecessarily।
Labels
Heart, pericardial sinus, ophthalmic/anterior arteries, posterior abdominal artery, sternal artery where demonstrable.
3. Cockroach — Nervous System
Aim
Brain, circumoesophageal connectives, suboesophageal ganglion এবং double ventral nerve cord expose করা।
Display sequence
- Dorsal dissection দিয়ে alimentary canal gently remove/displace।
- Head region-এ cerebral ganglia identify।
- Circumoesophageal connectives trace।
- Suboesophageal ganglion থেকে paired ventral nerve cords follow।
- Thoracic and abdominal ganglia serially identify।
Labels
Brain, circumoesophageal connectives, suboesophageal ganglion, thoracic ganglia, abdominal ganglia, ventral nerve cord.
4. Grasshopper — Nervous System
Cockroach-এর একই general logic, তবে body proportions আলাদা।
Display:
- brain;
- suboesophageal ganglion;
- thoracic ganglia;
- abdominal ganglia;
- paired longitudinal connectives.
5. Prawn — Nervous System
Main structures
Supraoesophageal ganglion (brain), circumoesophageal connectives, suboesophageal ganglion, thoracic ganglionic mass, abdominal nerve cord/ganglia.
Technique principle
Digestive tract এবং ventral tissues carefully displace করে nerve chain expose করবে; abdomen-এ ventral midline follow করা সহজ।
6. Pila — Nervous System
Diagnostic feature
Gastropod torsion-এর context-এ ganglionic nervous system; cerebral, pleural, pedal, buccal এবং visceral ganglia/connectives।
Display targets
- cerebral ganglia;
- buccal ganglia;
- pedal ganglia;
- pleural ganglia;
- visceral loop/connectives.
Common error
Connective vs commissure গুলিয়ে ফেলা: same-side ganglia linking = connective; paired opposite ganglia linking = commissure.
7. Lamellidens — Nervous System
Display targets
- cerebral/ cerebropleural ganglia near mouth;
- pedal ganglia in foot;
- visceral ganglia posteriorly;
- longitudinal connectives.
Bivalve nervous system dispersed; gastropod-এর মতো compact brain expect করবে না।
8. Earthworm — Reproductive System
Main structures
Testes/testis sacs (small, anterior), seminal vesicles, spermathecae, ovaries, oviducts, male ducts, prostate glands (species-specific practical), genital pores.
Display logic
Anterior reproductive segments carefully expose; gut সম্পূর্ণ remove না করে structures side-by-side demonstrate করবে।
9. Cockroach — Reproductive System
Male
Paired testes, vasa deferentia, seminal vesicles, ejaculatory duct, mushroom/accessory glands, genital pouch/phallomeres.
Female
Paired ovaries (ovarioles), lateral oviducts, common oviduct/vagina, spermatheca, collateral/accessory glands.
Key comparison
Male: slender ducts + accessory glands.
Female: conspicuous ovaries with multiple ovarioles.
10. Grasshopper — Reproductive System
Male
Testes, vasa deferentia, seminal vesicles/accessory glands, ejaculatory duct.
Female
Ovaries with ovarioles, lateral oviducts, common oviduct, spermatheca and accessory glands.
11. Prawn — Reproductive System
Male
Paired testes, vasa deferentia, terminal male genital openings (species/group dependent).
Female
Paired/connected ovary dorsal to hepatopancreatic region, oviducts, female genital openings.
Sex clue
Pleopod modifications and genital pore positions can support sex identification.
C. Minor Dissections
12. Prawn — Digestive System
Label: mouth, oesophagus, cardiac stomach, pyloric stomach, hepatopancreas, midgut/intestine, rectum, anus.
13. Pila — Digestive System
Label: mouth/buccal mass, oesophagus, stomach, digestive gland, intestine, rectum, anus. Radula belongs to buccal apparatus and may be separately demonstrated.
14. Lamellidens — Digestive System
Label: mouth, oesophagus, stomach, digestive diverticula, intestine, rectum, anus. Note: bivalves lack a radula.
15–17. Minor Nervous-system Displays
Cockroach, grasshopper and prawn-এর জন্য major-dissection page-এর same anatomy ব্যবহার করবে, কিন্তু minor display-এ clean exposure + principal labels-এ focus থাকবে; unnecessary fine branches chase করবে না।
Dissection Drawing Template
Every drawing:
- title;
- dorsal/ventral orientation;
- anterior/posterior direction;
- 6–12 essential labels;
- clean single lines;
- no artistic shading;
- scale not mandatory unless department asks.
Practical Viva Questions
- Why must earthworm circulatory dissection begin dorsally?
- Open circulatory system বললেও prawn-এর heart ও arteries কেন clearly visible?
- Insect ventral nerve cord chordate dorsal nerve cord থেকে কীভাবে আলাদা?
- Pila nervous system-এ torsion-এর historical anatomical effect কী?
- Bivalve Lamellidens-এ radula কেন নেই?
- Male vs female cockroach reproductive system-এর fastest visible distinction কী?