A Contribut. to the Embryol., Life-histoiy, and Classitìeat. of the Dicyemids. 57 



water, the larger fore end of the embryo describing a spirai while rota- 

 ting. In no case bave I succeeded in keeping them alive 48 hours. At 

 the end of 24 hours many are nsually foimd dead, or nearly so, the rest 

 siirviving ouly a few hours. The refractive bodies remain apparently 

 unchanged for some time after death and after the disintegration of the 

 other parts. I bave not seeu that the Dicyemids die sooner than the 

 infusoriform embiyos. 



If the renai fluid contains a large admixture of sea-water, as main- 

 tained by Vigelius (52), it is not at ali surprising that both embryos 

 and adiilts live for a considerable time in nearly pure sea-v^ater. But 

 if the infusoriform embryos are able to live much longer than the vermi- 

 form embryos and the adults , as Van Benedens experiments seem to 

 show, this fact alone would establish a very strong probability in favor 

 of the opinion that they serve to carry the species to new hosts. It is 

 possible, however, that the vermiform embryos fulfill this office, in which 

 case the infusoriform embryos could only be interpreted as males. This 

 alternative view is the one now entertained by Van Beneden (2). 

 There can be little doubt that one or the other of these views is correct ; 

 but the probabilities are so evenly balanced that it is diftìcult to become 

 a partisan of either. The researcbes of Giard (14 — 16) . Metschnikoff 

 (17 — 19), and Jülin (20 — 21) make it clear that the Orthonectidae 

 are closely related to the Dicyemids ; but the parallel between them 

 with respect to the phenomena of reproduction is not so complete as 

 represented by Van Beneden and Julin , even if we may assume that 

 the infusoriform embryo is a male. The following summary of conclu- 

 sions arrived at by Julin , will show some weak points in the argument 

 from anaiogy. 



1 . There are three distinct kinds of adult individuals , one male 

 and two female. Both female forms arise from the egg.s of the so-called 

 fiat female (»forme aplatie«), the males alone being produced by the 

 cylindrical female (»forme cylindrique«) . 



2. The distinctions between the females are slight compared with 

 those between the two sexes. Their origin and earlier stages of devel- 

 opment are the same , and it is only at a comparatively late date that 

 it becomes possible to distinguish them , by a peculiarity of unknown 

 significance, which appears only in the flat female. This peculiarity 

 arises in the form of a cell-like body located near the anterior end, be- 

 tween the ectoderm and the cell-layer which later becomes the muscular 

 layer. Metschnikoff suggests that this body ("Sub-polar cells«) may 

 represent a rudimentary digestive tube. 



