708 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the Gymnolmmata there is, in addition, an endothelial investment sur- 
rounding the enteron ; and in the Phylactolsemata a mesodermal 
epithelium is applied to the ectoderm. 
After some remarks on the phylogeny of the Bryozoa, which is a 
peculiarly difficult problem, Dr. Seeliger points out that the processes 
of gemmation in the Bryozoa show how tissues which are, histologically, 
very definitely differentiated, may again take on quite an embryonic 
character. In them, as in the budding Tunicata, no support is to be 
found for the doctrines of Heredity propounded by Weismann. The 
author says that he has sought for but has not been able to find any 
evidence of a removal of histogenetic plasma from the ectodermal cells 
that form the polypide-invagination, which might render explicable the 
return to embryonic relations. 
Larva of Flustrella hispida.* — Dr. H. Prouho finds that the larva 
of this Bryozoon has the same plan of organization as that of the 
cheilostomatous forms and as the larva of Alcyonidium mytili. The 
most striking points in its structure are the presence of two chitinous 
valves covering the aboral region, the differentiation of the mesoderm 
into numerous muscles and cellular layers, the most important of which 
is situated immediately below the aboral ectoderm, the presence of a 
nervous system, and the reduction of the hood to a sensory button or 
aboral organ which is connected with the pyriform organ by a musculo- 
nervous tract. Several of these characters ally the creature to Cyplio- 
nautes comjpressus. The larva possesses two kinds of organs ; those 
which, during metamorphosis, pass directly to the primary zooecium and 
appear to be of no use to the free larva, and those which perform func- 
tions useful to the free larva, and are destroyed when larval life ceases ; 
they are utilized by the primary individual as reserve nutriment. The 
internal sac and the parietal muscles belong to the former category, 
while to the latter three belong the pyriform and aboral organs and 
the corona. 
The fixation of the larva is effected, as in all larvae that are provided 
with an internal sac, by the evagination of that organ. The corona, the 
pyriform organ, and all the integuments, are retracted to the interior ; 
the aboral organ is invaginated below the ectoderm, and the larval 
organism becomes a closed sac, the free or frontal wall of which is 
formed by the aboral ectoderm of the free larva, while the basal part 
is formed by the internal sac. 
As soon as the free larva has become fixed, the phenomenon of 
histolysis commences ; this disorganizes much of the larval tissues and 
converts them into a number of nucleated spheres or histolytes, which 
become intermingled with the yolk-spheres and are, like them, put to 
use by the young polypide. The larval tissues which undergo histolysis 
are the nervous system, all the muscles except the parietal, the pyriform 
organ, the corona, the aboral organ, and all the oral integuments. The 
larva then passes into the cystid-stage. 
The ectoderm of the cystid secretes a thick cuticle which forms the 
entocyst of the primary chamber ; the aboral mesodermic layer becomes 
fused with the corresponding membrane which invests the internal 6ac 
Arch. Zool. Expe'r. et Gen., viii. (1890) pp. 409-59 (3 pis.). 
