IV 



ADVERTISEMENT. 



of a tentacle, a colletocystopborr, and a genital sac;" on the "young one-fifth of 

 an inch across;"' and on the "young six twenty-fifths of an inch across." 



In a fourth chapter, in an " histology of HaJichjstus auricula," the tissues of 

 the several parts of the body are considered— that is, " the umbellar and pedun^ 

 cular walls ;" " histology of the tentacles ;" " histology of the colletocystophores" 

 (anchors); " histology of the caudal disk;" and " histology of the digituli" and 

 " the prehensile cysts" (nematocysts and coUetocysts). 



AVith profound regret, we have to announce that before the completion of the 

 enoraviuT of the necessary plates to illustrate his work, Professor Henry James 

 Clark was called from this life, in the flower of his age, and in the midst of a series 

 of successful investigations. 



The publication of this memoir has, consequently, been greatly delayed. The 

 reading of the proofs and supervision of the work were kindly undertaken by Pro- 

 fessor A. E. Verrill, of Yale College, who has, however, himself been much 

 hindered in his work by ill-health and other causes. In editing this memoir he 

 has not thought it desirable to make any changes, except verbal and typographical 

 ones, which would not alter the meaning of the author. This has been carefully 

 adhered to in all cases, even where changes would, perhaps, have been made by 

 the autlior himself, had he lived, in consequence of the advance of knowledge 

 during the several years that have elapsed since the memoir was written. Owing 

 to the fact tliat the plates, with one exception, were engraved in Paris, and no 

 proofs were submitted for correction, several errors, noticed in the explanations, 

 were made in the lettering. These might lead to mistakes, in some cases, unless 

 their existence be noted. 



The following extracts from a Memoir of Mr. Clark, read by Professor A. S. 

 Packard, Jr., before the National Academy of Sciences, in 1874, will be of interest 

 to the readers of the present work : — 



" Within the year past we have lost a member who may be said, without dispar- 

 agement to others laboring in the same field, to have been the foremost American 

 histologist and microscopist, and one of our most skilful and accomplished biolo- 

 gists; one the rule of whose scientific life was a practical application of experi- 

 mental philosophy. A true naturalist, he was an enthusiast, and yet in his methods 

 of study severe, exact, and in all respects scholarly. 



Henry James Clark was born June 22, 1826, at Easton, Massactiusetts. Of his 

 early life little information has been obtained, except that he was fond of drawing, 

 an art which proved of much service and credit to him in after years. 



He received his collegiate education at the University of the City of New York, 

 graduating in 1848. 



