18 FRANCIS H. WELCH. 
channel; between the upper bulbous end of uterus and the 
upper boundary of segment are also ovarian glands. At the 
590th segment the zooid may be declared adult with full 
developed male and female generative systems, the latter 
from the uterus inclusive to its coecal offshoots as ovarian 
glands filled with immature vitelline masses; the length of 
such a segment would be + of its breadth, the anatomical 
details would coincide with the description already given of 
the several components of the segment under the respective 
headings. At the 690th segment, rather broader than long, 
fully developed ova are present in all the female passages 
except the vagina; the animal is mature. From this point 
the male generative system atrophies, and it is a difficulty to 
find a seminal gland, the segments markedly elongate and 
the uterus straightens, the lowermost prepare for separation 
from the parent stem. 
The dropping off of the over-ripe segment, so far as the 
eye can trace it, consists of a gradual thinning and lengthen- 
ing out of the upper half reaching its acme at the portion 
invaginated in the lower half of the preceding segment, 
until the line of junction is reduced to a mere thin film of 
tissue ready to give way on the slightest external force; the 
lower half of the segment from the genital orifice downwards 
undergoes but little, if any, change. More minute exami- 
nation reveals that the line of rupture takes place through 
the fibrous diaphragm dividing the segments, a point where 
the calcareous granules in the body substance are in a 
minority, and the point where separation takes place when 
force is applied to the zooids in continuity and in a mature 
district of the colony. ‘The transverse water-vascular canal 
is encroached on, and all but obliterated by the distended 
ovarian glands abutting on it, the ovarian follicles in the 
upper half coalesce by disintegration and rupture of the 
intervening substance so that the ripe ova lie free in the 
ragged space ; soon the corium is the only retaining link, and 
ultimately this gives way, allowing the segment, with its 
upper half free to discharge ova and its lower half com- 
paratively intact; to be carried out of the host with the fecal 
excreta. 
From these details it will be apparent that the develop- 
mental process mainly concerns the generative systems, the 
body structures deviating but little except in bulk in any 
part of the colony ; also that the formation of the body struc- 
ture and the separation of it into successive zooids precedes 
the development of the viscera. It will also be observed 
that the first appearance of the visceral components was in 
