60 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Morphology and Embryology of a Tardigrade.* — Dr. E. v. 
Erlanger has studied Macrobiotus macronyx Duj., which was fairly 
abundant in the Altrhein at Neuhofen in January and March 1895. 
Free balls of eggs were frequent ; the males were almost as common as 
the females (while in terrestrial forms they are rare) ; the males are 
about a half smaller than the females, more mobile, much more trans- 
parent, and colourless ; the spermatozoa are simply thread-like ; no 
copulatory organ was observed. The spermatozoa ejected near the 
posterior end of the females are sucked into the chitinous hind- gut and 
thence passed to the eggs, which occupy a space in the posterior half of 
the chitinous shell, left empty by the retraction of the body to half its 
usual length. The eggs are laid per anurn and have no membrane 
until fertilisation. Two polar bodies and the union of the two nuclei 
in fertilisation were observed. Sometimes both polar bodies divide into 
two, and the four may persist to the 16-cell stage. The first cleavage 
is at right angles to the longitudinal axis ; then one of the two blasto- 
meres divides, at right angles to the long axis and to the first plane ; 
then the second does the same ; then all four divide simultaneously ; 
the 16-cell stage and the 32-cell stage are similarly attained. A 
blastula with an excentric segmentation cavity results in about 36 hours. 
Before leaving the egg-membrane, the ovum has formed blood-cells. 
The membrane is burst by powerful contractions of the body and the 
boring action of the teeth. In the newly hatched young the glands of 
the appendages, arising from the coelom-sacs, are relatively very large 
and open between the claws. Development on to hatching takes about 
12 days at the temperature of a room, about 20 days in the river. The 
adults do not survive desiccation, as the terrestrial forms do. 
Anatomy of Thyas petrophilus.j — Mr. A. D. Michael gives a full 
account of the internal anatomy of an unrecorded Hydrachnid found in 
the neighbourhood of the Land’s End. The creature occupies a some- 
what curious habitat, for it was found in a very small stream of fresh 
water in such a place that, when the wind was on shore and the sea at 
all rough, considerable quantities of salt water must be carried into the 
stream. Although a water-mite, it is not found swimming ; like other 
members of its group, it is adapted for crawling only. Mr. Michael 
invariably found it either in some chinks and splits in the rock, where 
it can only be discovered by carefully chiselling away the rock in likely 
places, or clinging to the under side of large stones lying in deep pools. 
When its hiding-place is discovered the mite is very conspicuous. It 
is of a beautiful scarlet colour, shaded and varied with orange. Most of 
the joints of the legs are furnished with a radiating whorl of large yellow 
spines tipped with scarlet, which give it a very brilliant appearance. 
The colours are very difficult to preserve after death. The alimentary 
canal of the new species differs considerably from everything which, to 
the author’s knowledge, has been described in the family, or indeed in 
the Acarina at all ; of course, however, it is a modification of the 
general plan. This the author describes in considerable detail. Like 
the alimentary, the male reproductive system differs in a remarkable 
degree from anything which has, to Mr. Michael’s knowledge, been 
* Biol. Centralbl., xv. (1895) pp. 772-7. 
f Proc. Zool. Soc., 1895, pp. 174-209 (3 pis.). 
