622 SUMMARY OF CURRENT RESEARCHES RELATING TO 



panion, but here, as elsewhere, two kinds of females can be distin- 

 guished — tbe nematogenous and the rhombogeuous. The former have 

 a body of very variable external appearance ; it may be elongated, 

 irregularly rounded, claviforrn, much swollen at one extremity, or 

 attenuated at both. Four granular lobes can always be distinguished, 

 and these, although they vary much in form in different individuals, 

 are always formed of a single cell, just as are the two lobes in 

 Dicyema. As in other Dicyemidse, there is a cortical layer and an 

 axial or medullary body. The former is made up of a small number 

 of epithelial cells, set in a single layer, and so touching one another 

 as to form a continuous membrane, which completely shuts in the 

 medullary portion. Each cell is ciliated in youth, and smooth when 

 adult. It is not possible, as in Dicyema, to distinguish polar and 

 parapolar cells, there being no cephalic tuft. As may be supposed, 

 the medullary body consists of a single cell. In this there are to be 

 found germs and embryos at every stage in development. It varies 

 greatly in form, but is always limited by a firm layer of protoplasm, 

 of equal thickness throughout its whole extent, and always capable of 

 allowing of the passage of the contained embryos. The nucleus is 

 generally oval, has a distinct limiting membrane, and is traversed by 

 a nucleoplasmatic reticulum. 



When the embryo is on the point of leaving its parent it presents 

 a convex and almost hemispherical hinder face. It is about one and a 

 half times as long as it is wide, and a short way from the anterior end 

 there is a circular constriction which has sometimes the appearance of 

 a rather deep groove. It is covered by vibratile cilia, by the aid of 

 which it swims freely in the liquid of the corpus spongiosum, when it 

 has made its way out of its parent, and in thus moving it describes a 

 spiral. The cuneiform embryo of Conocyema, like the vermiform one 

 of Dicyema, has a large central cell, and a peripheral epithelial invest- 

 ment ; but while in the latter it is always fusiform or cylindrical, it is 

 here always spherical. Among the outer cells the four apical ones 

 may always be distinguished. The embryos, with these characters, 

 are all developed from monocellular germs, which have all the signs 

 of true ovules. These divide into two, and then into four blastomeres, 

 one of which is often very much larger than the rest. In the next 

 stage there are six small and one large cell, and then we have an 

 epibolic gastrula. The six smaller outer cells dividing, we get thir- 

 teen in all, which is the number characteristic of the adult. The 

 cuneiform embryo escapes to the exterior by perforating the body of 

 its mother, the four apical cells become charged with granules, the 

 axial cell becomes enormously developed, and new germs appear. 



After pointing out briefly the characters of the rhombogeuous form, 

 Professor van Beneden passes to Microcyema vespa, the small embryo 

 of which was taken by G. Wagener for the infusoriform embryo of 

 Dicyema gracile. It is divided into two parts by a median constric- 

 tion ; the hinder of these consists of an axial fusiform cell, and of two 

 others which completely envelope it. The anterior end of the central 

 cell projects into the anterior segment, where there is also a granular 

 mass and a cortical layer, formed of two clear cells similar to those 



