ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
41 
a very general capacity for cross-fertilisation, and in tlie case of at least 
one hybrid ( J Echinus £ -Strongylocentrotus $ ) cross-fertilisation takes 
place with greater ease, and produces larvae of larger size, than direct 
fertilisation. 
As a rule the hybrid larvae are of the maternal type, but some species 
have a much greater potency than others in the transmission of their 
characteristics. “The Strongylocentrotus % -Sphser echinus £ hybrid is 
formed only at the time when the Strong ylocentrotus ova have reached 
their minimum of maturity ; whilst in the case of the reciprocal hybrid 
it follows that, as the maturity of the Strongylocentrotus sperm increases, 
it is able to transmute first a portion and then the whole of the hybrid 
larvae from Sphserechinus to its own type. In other words, the charac- 
teristics of the hybrid offspring depend directly on the relative degrees of 
maturity of the sexual products.' 1 ' 1 
Ccelentera. 
Mesenteries and Siphonoglyphs in Metridium marginatum Milne- 
Edwards.* — Mr. G. H. Parker has investigated certain structural pecu- 
liarities in a single species of Actinian, Metridium marginatum Milne- 
Edwards, as represented by 131 adult specimens. He found that uni- 
formity of structure was by no means a characteristic of the species. Of 
the specimens examined 77 had only one siphonoglyph, 53 had two, and 
a single individual possessed three such organs. This last must be con- 
sidered exceptional, but the other two may fairly be regarded as typical, 
and may be styled the monoglyphic and diglyphic types. Such variation 
in the number of siphonoglyphs is not unusual among other Actinians, 
though it may not often be so pronounced. There is an exact correlation 
between the number of siphonoglyphs and of directive mesenteries, 
each siphonoglyph, even in the exceptional case of three, having one 
pair of directives attached to it. The non-directive mesenteries vary 
greatly in number. In the diglyphic type there were from four to ten 
pairs of non-directives, though the great majority had four pairs arranged 
in two groups of two pairs each, which is the assumed typical Hexactinian 
arrangement. 
In the monoglyphic type there were from three to fourteen pairs of 
non-directives, and the great majority could be relegated to one of three 
structural sub-types characterised by five, six, and seven pairs respec- 
tively. The most important point in connection with the variations of 
the incomplete mesenteries was that, of the 131 specimens examined, no 
two were alike. Mr. Parker emphasises the necessity for examining a 
large number of specimens when investigating Actinians, that the pos- 
sible error of regarding individual variations as characteristic of large 
groups may be avoided. 
Protozoa. 
New Amoeba in Man.f — Prof. I. Ijima reports what seems to be a 
hitherto undescribed species of Rliizopod parasite in man. This parasite 
(Amoeba, miurai ) was found in abundance in the serous fluid accumula- 
tion of the peritoneal and pleural cavities in a case of peritonitis and 
* C.Z. Harvard, xxx. No. 5 (1897) pp. 259-72 (1 ph). 
t Annot. Zooh Japon., ii. (1898) pp. 85-94 (9 figs.). 
