الفهرس 
The reproductive systemOnly 14 pages are availabe for public view
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Abstract
Samples of P. radiata were collected from Abo-Qir (Alexandria) where they were found attached to rocks , while the other samples A. rubens were collected from the River Nile’s branch (El-Gharbia) where they burrow in mud . The collection of samples is occurred from October, 1993 till September , 1994 . The presnt study includes two main items : P. The reproductive system : It is concerned with reproductive biology and includes the developing of gametes and reproductive cycle using histology and histochemistry stains , and ultrastructure of mature sperm . The results of this part can be summarized as following : - The comparative study of male and female of’the two species showed a great difference in developing of gametes , their shedding times and their mode of fertilization . - The two investingated species have two spawnings a year , the first one is in autumn and the second is in summer . - Synchronization was observed in the gonads of P. radiata ,while in A. rubens sperms are shed in water although the ova remained in the gill plates where they are fertilized , then incubated till larvae grow.