360 Mr H. Robinson, On the Formation [May 20, 
internal, and is effected by the thrusting of the penis through any 
part of the skin of the female. 
The second ciliated ring of the head is composed of three rows 
of cilia, and appears to be the homologue of the prae-oral band 
of a Trochosphere. The nephridia which constitute the first pair 
correspond in position and in structure to the head-kidneys of a 
Trochosphere. 
(4) On the Formation of Struvite by Micro-organisms. By H. 
Ropinson, M.A., Downing College. 
I wish to call the attention of the Society to the formation of 
Struvite, or ammonium-magnesium phosphate, or—as it is some- 
times called—triple- -phosphate by micro-organisms when they are 
cultivated in nutrient gelatin and agar-agar. Last November I 
noticed, for the first time, in several tubes of nutrient gelatin in 
which pure cultivations of micro-organisms had been growing for a 
long time, fine, bright, well-formed crystals. I could not get the 
micro-organism producing the finest crystals to grow in another 
tube; but a second, the Bacterium putidum fluorescens, when 
transferred to a tube of agar-agar grew well and produced crystals 
in abundance and very rapidly. This specimen I obtained from 
a Cambridge well water in February, 1888, and it had been grown 
in tube after tube from that time. I had at the same time 
another specimen of the same bacterium which Mr Adami had 
given me; so to make sure the crystals were really produced by 
the micro-organisms and not by any spontaneous change of the 
nutrient substance I determined to make some experiments with 
both specimens, and in two lots of agar-agar rather differently 
prepared. I therefore inoculated four tubes with one specimen 
and four with the other; in each set of experiments one tube was 
prepared from agar-agar, infusion of beef, peptone and salt in the 
usual way, and the three others with agar-agar, Liebig’s extract, 
peptone and salt. In three days all the four tubes inoculated 
with my own bacterium showed a good crop of crystals; but it 
was not until the ninth day Mr Adami’ bacterium succeeded in 
producing any, and then only in one tube— an extract of meat tube. 
On the nineteenth day two more tubes—the one made with in- 
fusion of beef, and another meat extract tube—contained crystals, 
but 1t was a week longer before I noticed any in the last of the 
four tubes. At this time Mr Adamr’s bacterium grew much more 
luxuriantly and produced more green colouring matter than my 
own; but in more recent cultivations of the two specimens I have 
not found this difference between them, or in their power to pro- 
duce crystals. 
I have isolated another micro-organism, I think a bacillus— 
spore-forming—in which also the ability to cause the formation 
