EMBRYOLOGY. 
Tun. 5 
C.— EMBRYOLOGY. 
Salensky (23) come3 to the conclusion that the sense-vesicle of the 
Ascidian larva’s nervous system is homologous with the epiphysis of 
Yertebrates, and the Ascidian eye with the parietal eye. 
Seeliger (28) discusses the origin of the cells of the test, and confirms 
Kowalevsky’s results. In Oikopleura cophoccrca , however, he finds that 
ectoderm cells pass into the “ Haus,” and no mesoderm cells. In both 
Salpa democratica and Clavclina lepadiformis migrating mesoderm cells 
wero found (soo also Ritter, above). 
Salensky (24) comes to the following conclusions : — (1) The original 
form of metagenesis in the Tunicata is represented in such Synascidian 
genera as in the larval condition are able to reproduce themselves 
sexually ; (2) Amongst known Synascidians Distaplia alone represents an 
alternation of generations, while the development of the Didemnidce has 
nothing to do with alternation of generations ; (3) The primordial bud 
of the Distaplia larva should be regarded as a transition form between 
the simple bud and the proliferous stolon of the metagenetic Tunicata ; 
(4) The proliferous stolon is derived from the bud which, before separa- 
tion from the maternal body, began itself to divide or bud ; (5) In the 
oldest metagenetic forms the “ nurse,” after the production of the sexual 
generation, viz., the buds, must die ; in the further development of meta- 
genesis, the life of the nurse is always more prolonged. Doliolum repre- 
sents in this connection a transition form between the Synascidians and 
Salpa. 
The development of Salpa, both sexually from the embryo and also 
asexually by budding from the stolon, is discussed and described very 
fully by Brooks (5), as well as the organogeny, and the foetal membranes 
and appendages. 
Davidoff (6) has a short note on the neurenteric canal of the Ascidian 
embryo. 
IIjort (12) treats of the developmental cycle in the Compound 
Ascidians ; and Pizon (21) also deals with the subject, specially in the 
Botryllidm. 
Willey (33), in his Studies on the Protochordata (1), comes to the 
following morphological conclusions : — That the first four primary stig- 
mata of Ciona , and probably also of Ascidia mentula , &c., represent and 
are derived from one primitive gill slit, and that three pairs of gill slits 
are formed altogether in Ciona, & c., and that all the stigmata of the adult 
branchial sac are derived from and represent these six primary stigmata. 
New transverse rows of stigmata arise by division of the pre-existing 
transverse rows. The long axis of the adult Ascidian is at right angles 
to the long axis of the larva. The atrial cavities are ectodermal invagi- 
nations. The pyloric gland of the Ascidian is homologous with the 
hepatic csecum of Amphioxus. Appendicular ia is, he considers, not a 
primitive form, but represents a larval Ascidian which has secondarily 
