The present title "Chordata-I" has been designed to approach the morphology, anatomy, physiology and development of the forms prescribed in the syllabus for the undergraduate students of Bangalore University. The subject matter has been discussed in a coherent way since it is most natural for a student in studying the architectural elements of an animal body in the quest to know how they function. This text intends, therefore, to enable the student, through his own natural appetency, to correlate form and function so that he possesses for subsequent work in either anatomy or physiology a firm foundation for a real edifice of knowledge. The book is a comprehensive guide, though it does not burdon the primary aim throughout has been clearity so as to make the text selective and meaningful. IT provides a nucleus around which the teacher can play a successful cause without too much learning on complementary and supplementary readings.