8 CHARLES BADHAM. 
about Abranchus (a genus allied to Austrobdella), corre- 
lates tlie fact that the members of fliis genus are unable tb 
swim, with the fact that they infest fish which live in shallow 
water among algal growths and so afford an opportunity for 
leeches to creep on to them. He also supposes that when the 
time comes for depositing the cocoon Abranchus drops to 
the bottom and fixes its cocoon in seaweed. I have not 
ascertained the method of depositing the cocoon in Austrob- 
della, but would point out that the fish on which it lives 
gets a great deal of its food by burrowing in the sand. 
Annulation. 
. 
A typical somite consists of 'three annuli, and in the adult 
these three annuli are divided so that the somite is of six 
annuli. In young forms the somite consists of the three 
primitive annuli ; this is followed by a stage in which there 
are five annuli to the somite, due to the division of the annuli 
anterior and posterior to the annulus in which the nerve 
ganglion is situated. This stage of five annuli to the somite 
“may persist in specimens which are quite large, but in the 
largest specimens all the somites in the testicular region have 
six annuli. Thus it happens that specimens 6 mm. in length 
are seen, in which the primitive annulus containing the nerve 
ganglion is still undivided. It is owing also to this subse- 
quent division of primitive annuli that a difficuly arises in 
regard to the number of annuli to be seen in the neck region, 
for these increase in number with the length of the specimen. 
In a leech of 4 mm. the male pore is between the 15th and 
:16th primitive annuli and the female pore between the 17th 
and 18th annuli. At this stage the somite in the testicular 
region is still trimerous. In a leech of about 9 mm. there 
are found twenty-three or twenty-four annuli in front of the 
male pore. The primitive annuli which divide to form the 
new annuli are the 4th, 5th, 7th, 10th, 11th, 13th, 14th, and 
15th (Text-fig. 2). In regard to the total number of annuli, 
my determinations have been varied owing to the fact that 
