STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 319 
is reached. The larval Phoronis resembles Loxosoma in 
the possession of a ventral flexure of the alimentary canal, the 
dorsal gut-flexure of the adult being entirely unrepresented in 
the Entoprocta. Thus the epistome of Polyzoa is ventral, 
and the ganglion developed in its neighbourhood is to be homo- 
logised with the pedal ganglion of Molluscs rather than with 
the brain of Phoronis. 
The vascular system of Phoronis is entirely unrepresented 
in the Entoprocta, whilst the asymmetrical generative organs 
of the former differ markedly from the simple paired gonads 
of the Entoprocta. The four divisions of the alimentary 
canal, characteristic, according to Caldwell, of Phoronis and 
Brachiopoda alike, are not represented in the Polyzoa, 
whilst the nervous system, which in Phoronis consists of a 
plexus of fibres and cells lying outside the basement membrane 
of the epidermis, and concentrated in certain definite regions, 
is in striking contrast with that of Loxosoma. It seems to me, 
in fact, that a comparison between the adult Phoronis and 
Loxosoma is exceedingly difficult, whereas in many of the 
Trochosphere characters of the larvae it is easy to point to 
parallels in the two genera. 
It is not altogether impossible that the invagination occur- 
ring on the ventral side of Actinotrocha, and subsequently 
evaginated to form the foot or body of the adult Phoronis, may 
be represented by the vestibular invaginations of Loxosoma. 
In the Ectoprocta, according to the researches of Barrois, 
fixation universally takes place by the evagination of the 
“ internal sac” (the homologue of the vestibular invagina- 
tions). If instead of losing their stomach at an early period 
of development the Ectoproctan larvae retained this organ, 
and became adult, it would not be impossible for the gut to 
pass into the evaginated “ internal sac,” and thus to reverse its 
former curvature, as in the case of Phoronis. I believe that 
the question of the relationship of the Polyzoa to the 
Brachiopoda can only be satisfactorily resolved by a re- 
newed study of the embryology of the latter. Caldwell has 
laid special stress on the resemblances between Brachiopoda 
