though incomplete account of the embryology of the squid, "The Development 

 of the Squid", was published in the same year by W. K. Brooks, and eight 

 years later S. Watase issued his beautiful work upon the segmentation of the 

 ovum and the homology of the germ layers. The embryology and organogeny 

 of the common European species, Loligo vulgaris, have been carefully studied 

 by KoLLiKEE , Faussek , BoBRETZKY , KoRSGHELT and others. Furthermore 

 comparative studies of various organs of the Cephalopoda (not including this 

 species) have been published. The reproductive system of Cephalopoda has been 

 described by J. Brock ; the coelom by Grobben ; the gills by Joubin : the ink sac 

 by GiROD ; and the skin ^chromatophores) by Girod , Physalix , Rabl, Chun and 

 others. However, a large amount of work yet remains to be done upon the 

 organogeny, anatomy and physiology of the squid. In this work, the vascular, 

 alimentary and nervous systems have received especial attention, but an eflfort 

 has also been made to give a full account of the gross anatomy of the squid. 

 In the work dissection has been supplemented by the study of a number of 

 serial sections of embryos , of young squid and of adult tissues. The squid studied 

 were obtained at Woods Hole, Mass. and at Elberon, N. J. The work was 

 done at Princeton University , at the Marine Biological Laboratory , Woods Hole , 

 at Brown University, at the Harvard Medical School, and at the Woods Hole 

 Laboratory of the United States Fish Commission. I am especially indebted to 

 Professor Ulbic Dahlgren and to Dr. H. G. Bumpus for advice and assistance in 

 this work. 



This work , in a less complete form , was presented to the faculty of Brown 

 University in partial fulfilment of the requirements for the degree of Doctor of 

 Philosophy. 



Mr. W. T. Oliver, draughtsman, of Lynn, Mass. has redrawn or retouched 

 several of the figures. 



The class to which the Squid belongs, the Cephalopod Mollusc, is very highly 

 specialized. That this specialization shows itself in a very striking manner in 

 the general form of the Squid and in the position that it normally maintains , will 

 be readily seen after a glance at the diagrams of an unspecialized mollusc and 

 of the embryo of the Squid. 



The hypothetical unspecialized mollusc (text figure 1) is bilaterally symme- 

 trical, its back is convex, and its anterior end, bearing the mouth, the eyes, 

 and a pair of tentacles, forms a distinct head. The ventral portion of the body 

 is a thick , muscular plate , the foot , by means of which the animal creeps. 

 The upper part of the arched body contains the viscera and is called the visceral 

 dome. From the side of the visceral dome there arises a circular fold of skin, 



