-2 C. 0. Whitraan 



gard to their cycle of life , seemed to me to render further investigation 

 desirable , even if üothing more than a confirmatiou of results already 

 reached should be accomplislied. Although the questiou of cardinal inter- 

 est — the fate of the »Infusoriform embryo« — stili remains uusolved, 

 yet some faets of cousiderable importance bave been obtained. 



My study of the Dicyemids, begun in December, 1881, and contin- 

 ued imtil the end of Aprii of the current year , has been carried on in 

 the Zoological Station at Naples. For the opportunity and the rare facil- 

 ities for work which I bave enjoyed in this Institution, I am more 

 deeply indebted than any of the conventional forms of acknowledgment 

 would indicate. To pass over my obligations in silence might be con- 

 strued as a failnre to recognize tbem ; while any attempt to express 

 them would certainly seem inadequate to myself and extravagant to 

 those unacquainted V7ith the circumstances. I hope the acknowledgment 

 of the difficulty will be accepted as the best evidence 1 can, at present, 

 give of my appreeiation of the advantages enjoyed while at the Station, 

 and of my gratitude for the cordial and generous treatment received 

 from its Director and ali the gentlemen associated in its management. 



As to the direction my study has takeu, I may say that, at the 

 outset , I did not anticipate being drawn into systematic work : and, 

 had I foreseen the necessity for such work and the amount of time and 

 labor involved in it, it is more than probable that I should have devoted 

 my attention to another subject. Stili this porti on of my work has not 

 been ali drudgery. The accurate determination of species calls for a 

 careful discrimination between individuai peculi a ri ti es and 

 specific characters; and the range of va ri ahi li ty, in both 

 tliese respects , is a question not devoid of interest. 



The methods employed have been the same as those described by 

 Van Beneden. I have used acetic acid quite as much as osmic acid, 

 but hàve found it iraportant to watch the action of these re-agents on 

 fresh specimen«. I have found the picro-carmine solution described by 

 Mayer to be a very useful staining fluid. 



The matter to be dealt witli in this paper may be arranged under 

 four hcads : 



1. Classification, including historical and criticai remarks, 

 and systematic descriptions. 



2. Re production, embracing the pheuomena of transition from 

 the r bombo genie to the nemato genie condition , a comparison 

 of the Dicyemids with the Orthonectidae , and a general survey of the 

 evolutionary cycle, so far as at present known. 



