864 The American Naturalist. [October, 
occur while the egg is still in the “egg-ball.” It is not yet determined 
at what time the fertilization of the ovum takes place. In the case of 
E. acus the gastrula (larva with 6-8 hooks) goes through certain 
changes, in the body of the mother, which in other species are delayed 
until the. parasite arrives in an intermediate host. According to 
Hamann the nuclei of the ectoblast unite to form very large nuclei, 
the ectoblast being a syncytium. 
Ectoderm:—A. syncytium with large nuclear bodies which are 
amoeboid and give rise by direct division to the nuclei of the skin; the 
fibres in the skin are looked upon as elastic. The species Æ. claveceps 
is especially interesting: in this case the skin of the adult remains a 
syncytium with large nuclear bodies; author looks upon this as a case 
of paedogenesis. In other species the ectoderm separates into two 
layers: an outer layer with nuclei and elastic fibres, an inner 
layer in which the lacunes are formed. The lacunes of the 
skin and lemnisci form at the same time that the giant nuclei of 
the ectoderm divide into the skin-nuclei. The lemnisci arise as 
two lateral papille of ectodermal origin; these project into the body 
cavity; they are at first solid but when they have reached their full 
length a number of light colored spots became visible in their sub- 
stance; these spots grow more numerous, become connected and form 
the canal-system. In Æ. claveceps the lemnisci retain their larval 
character, being round with central canal and two very large nuclei. 
In other species the lemnisci are more highly developed; the canal- 
system is branched and numerous nuclei are present. The canal- 
system of the lemnisci, neck and rostellum unite in the circular canal 
and, according to Hamann (in agreement with Schneider but in 
opposition to Leuckart’s view), are entirely separated from the 
lacunes of the rest of the body. The lemnisci are compared with the 
ampullæ of the echinoderms. Hamann supposes them to aid in stretch- 
ing the rostellum and to act as a reservoir for the liquid when the 
rostellum is retracted. 
Entoderm :—In the early stages the entoderm is a solid mass, but as 
the parasite develops, an outer layer of cells separates from the central 
mass and forms an epithelial lining membrane for the body-cavity 
(coelom) ; the remaining cells give rise to the genital organs and the 
asara On the outer layer peripheral circular muscle fibrillæ form 
` in each cell, thus giving rise to epithelial-muscle cells of entodermal 
origin. Some of these cells leave their position in the epithelium and 
wander to its median surface where they assume a spindle shape 
give rise to the longitudinal muscles, which anastomose 
