On the Life-History and Development of the Genus Myzostoma. 545 



inconsiderable course of development, it does not include the whole, nor 

 even the most important part of the larvai history. This was no doubt 

 due to the smallness of the larvae to be dealt with, and the non-success 

 of all efiforts to obtain artificial fecundation. This bad fortune Metschni- 

 KOFF shared with Semper and Gkaff , neither of whom were able to 

 obtain results in this direction. In his monograph of the genus Graff 

 added but little to our knowledge of the development of the genus ; the 

 whole of his results under this head beiug contained in the following ^ : 

 »Und so sind es nur die Entwicklungszustände von 0,2 mm Länge an, 

 welche ich kenne. Doch gestatten auch diese einen kleinen Fortschritt 

 in der Erkenntnis der Entwicklungszustände unserer Thiere. Larven 

 von dieser Länge zeigen 3 bis 5 Fußpaare, terminalen Mund und After, 

 einen wohl ausgebildeten Bulbus musculosus und einfachen unverästel- 

 ten Magen.« 



I have had more good fortune in attempting to bridge over the gap 

 in our knowledge of the development, and have further been successful 

 in obtainiug artificial fecundation , to which success, no doubt , no in- 

 considerable portion of the results obtained is due. 



Such briefly was the state of our knowledge of the embryology of 

 the group , when at the dose of last year I began my researches. We 

 knew the segmentation fairly well by Metschnikoff's researches, and 

 we knew that a completely ciliated laiTa left the e^g. But beyond this 

 point the larvai history was totally unknown. Of the post-larval history 

 a fair proportion was known from the researches of Semper, Metschni- 

 KOFF and Graff , but this knowledge does not seem to have been 

 enough to determine even approximately the systematic position of the 

 genus. Metschnikoff, it is true, with his usuai perspicuity, was lead 

 by his researches to class the Myzostomidae among the Chaetopoda, and 

 indeed , as a special division Chaetopoda paralitica ; but while the 

 views of this distinguished zoologist were adopted by many others , iu- 

 cluding Claus in his Grundzüge der Zoologie 2, Prof. Graff in his 

 Monograph and later papers on the group regarded the genus as allied 

 to the Tardigrada and LinguatuUdae. With what justification we shall 

 see in the sequel. 



Methods of research. 



A few words on the methods employed may perhaps not be out of 

 place. The development was mainly studied on the living animai. Con- 



1 1. e. p. 66. 2 Vierte Auflage. 1880. p. 506. 



Mittheiluugen a. d. Zoolog. Station zu Neapel. Bd. V. 36 



