الفهرس 
Main taxonomical characters of ascidiansOnly 14 pages are availabe for public view
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Abstract
This work was prolonced froin J~me, 1982 till Idag 1983r A11 the specimens used were collected from the Eastern harb’o L~ of A1exm1dri.a . This thesiz comprises two parts. The f i r s t part 4eals with tile coizlparative liistolo~icala rd hi8tochemical st~ructures of tile -tv,;iic of abundant foulin:; ascidians t o j-llustrate, as f a r as p o s s i b l e , t h e arrangement and functioc of the various components of t h i s importent c h a r a c t e r i s t i c organ. Similarity between t h e histo1o~;icala ppearance of t h e a s c i d i a n t u n i c and t h a t of the vertebrate connective t i s s u e is discussed. Tiiis part of tlie study is a l s o planned t o a t t r a c t the attentior, t o the importance of h i s t o l o g i c a l and histocl~emical s t u d i e s of -6 ”.. marine organisms which may be used as a l t e r n a t i v e sources of food i n Egypt. As attempt has been made i n this part to record the types of blood c e l l s found i n the tunic o:P abundant; Zgyptian ascidians and compare them with other y-rtinent observations i n related ascidians. Iiloreover, resul-ks re la tin^ t o blood c e l l s d i s t r i b u t i o n , f ~uzctional si~gnificance and t h e i r r e l a t i o n t o various histocheinical reagents are discussed . The secona; part includes a detailed study of tlie predominant f oulin:: ascidian ”Styes pAaar_t;-i,tgw. The r e s u l t s of this (105 1 part could be surmmrized as follows: 23%- e la pa,i:;;n i s cons idered as -the most wide-spreacl ascidian of f oulin~i n t h e Ea s t e rn harbour of Alexan<rla. m- he sm-er months are the f lourishim: periods of t h i s nscidian species, The ~Wntle is a s o f t w a l l of the body, lying underneath the t e s t and encloses the i n t e r n a l organs. It is b u i l t up of t h r e e l a y e r s of a simple t i n,J n u e . The r e s p i r a t o r y and the alirentary system includes the branchial sac and the alimentary canal proper. It &\Tees in most of its d e t a i l s with the respiratary and alimentary system of s o l i t a r y ascidians. Some v a r i a t i o n s were observed i n the present species, these a r e r e s t r i c t e d i n 4x40 p o i n t s , The f i r s t i s t h a t the branchial sac of -Y&- tl~-el. n pa--r-t-i-t -a included t h e g r e a t e r part of t h e body and is made up of an hiunense pharynx begining between the branchial siphon f orniing a sac reachi~.; nearly t o the base. The second is that the alimentary canal proper is i n the f om of two U-shaped loops, one enclosing t h e other and l i e s on the l e f t side of the body. It includes t h e oesophagus, the sto~nach, the i n t e s t i n e and -the rectum which opens i n t o the cloaca1 cavity or atrial cavity by the anus at the dorsal margin of the body. 4) The endostyle is a long canal-shaped gland which runs along the e n t i r e v e n t r a l edge of the branchial sac. The sides and specially the f l o o r of the endostyle, are r i c h l y c i l i - a t e d , whi le tilere a r e f o u r stro_r,; lg marked, p e c u l i a r l y - shaped glandular t r a c t s , two on each side, running along its length separated by areas of closely-packed f usif om c e l l s with short c i l i a , among ahich a r e found some bipolar sensory c e l l s . 5) We w a l l of the branchial sac is penetrated by a large number of channels (bars) through which the blood flows. Some of which run i n one direction and soine i n another. 3etween these bars there a r e stigmata, by means of which t h e c u r r e n t of water passes from the branchial sac t o the l a r g e atrial cavity. 6) Five regions of the alimentary canal a r e e a s i l y distinguished on the b a s i s of t h e i r h i s t o l o g i c a l s t r u c t u r e . These regions a r e the branchial sac, a short tapering oesophagus, an ovoid ridged stomach, an i n t e s t i n e and the rectum. 7) The oesopilagus is a curved tapering tube running from the postero-dorsal region of the branchial basket till the stomach. Its l i n i n g epittielium has a number of four longi t u d i n a l grooves which form a l~men of the oesophagus.