396 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
New Cercaria from the Snail.* — Messrs. L. Vaney and A. Conte 
describe Cercaria pomatia sp. n., from the digestive gland of Helix 
pomatia. Sporocysts, cercariae, and young flukes were found. The 
authors refer to two previous records of distomatous parasites in flukes, 
by Meckel in 1846, and Siebold in 1854. 
Cestodes of Birds.f — Herr K. Wolff hugel discusses the ..systematic 
relations of Dicranotsenia , Drepanidotsenia , Hymenolepis, & c., and de- 
scribes Tsenia candelabraria and Fimbriaria malleus. 
Incertae Sedis. 
Life-History of Dicyema. J — Prof. W. M. Wheeler begins by giving 
a summary of our knowledge as to the structure and life-history of the 
Dicyemidae. It will be enough to recall that the axial cell of the fully 
formed Dicyemid always contains germ-cells or developing embryos, a 
study of which has led to the distinction of two very different lines 
of embryonic development in individuals of the same species. In some 
of the individuals the germ-cells develop into so-called vermiform, in 
others into so-called infusoriform embryos ; and although it has been 
shown (Whitman) that the parents of the two kinds of embryos are 
indistinguishable morphologically, it has, nevertheless, been found con- 
venient to give them different names. The mother of vermiform embryos 
is called a nematogen , the mother of infusoriform embryos a rhom - 
bogen. 
From observations on Dicyema coluber , Wheeler infers that the same 
animal is both nematogen and rhombogen at different periods of its life, 
and that it is first a nematogen and then a rhombogen (the reverse of 
Whitman’s sequence). He found about a dozen specimens (out of a 
large number) which contained both vermiform and infusoriform 
embryos in process of development, indicating a transition between 
the two reproductive phases. 
He agrees with Van Beneden in interpreting the so-called infusoria 
form embryo as the male Dicyemid, as is suggested by its resemblance 
to the male of the Orthonectidaa. The infusorigen or cell-mass which 
gives 'rise to and liberates the infusoriforms, has been regarded as an 
embryo (epibolic gastrula), the ectoderm cells of which are all germ- 
cells and give rise to the infusoriforms. “ On this supposition Dicyema 
performs on its offspring an experiment which some experimental em- 
bryologist would regard as impossible, since in this case, the gastrula 
is resolved into its component cells, each of which is capable of repro- 
ducing a whole organism.” Prof. Wheeler believes that the infusorigen 
may admit of a different interpretation. He finds a number of very 
deeply staining granules mingled with and adhering to the cells of 
the infusorigens. These granules closely resemble the minute bodies 
which were seen within the mature infusoriform, and may therefore be 
spermatozoa. “ If this is the case, the central cell of the infusorigen 
may represent a chemotactic centre which facilitates fertilisation by 
holding all the germ-cells together in a mass and by attracting the 
spermatozoa to the same point in the axial cell of the Dicyema” On. 
* Zool. Anzeig., xxii. (1S99) pp. 194-6 (2 fi^s.). f Tom. cit., pp. 217-23. 
X Torn, cit., pp. 169-76. 
