ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
773 
Dr. Eawitz also discusses the relation between sensory and secretory 
functions in the mantle-margin, and concludes that the differentiation of 
specific sense-organs is in inverse ratio to the glandular activity. Finally 
he emphasizes, not without cause, the necessity of distinguishing 
between the manner in which some animals are influenced by light and 
the manner in which others have sensations of light or it may be visual 
perceptions. Pigment-spots and pigment-cells have no sensations of 
light, far less power of sight, therefore it is unwarrantable to speak of 
them as “ primitive optic organs.” 
Molluscoida. 
a. Tunicata. 
Development of Stigmata in Ascidians.* — Mr. W. Garstang 
attempts to offer an aid to the solution of the problem which renders so 
difficult a comparison of the stigmata of fixed Ascidians with those of 
their pelagic allies. At the outset he found himself disinclined to 
accept the generally received view that the pelagic Caducichordate 
Tunicata have been derived from the so-called Compound Ascidians, 
and he studied, therefore, the development of the stigmata of the latter 
in the hope that in them recapitulative stages would be met with. 
Mr. Garstang has investigated Clavelina, and has nothing to add to or 
alter in Seeliger’s account published seven years ago. In Botryllus the 
two modes of development which are known to occur in Ascidians are 
to be seen ; the stigmata in the oozooid arise by the subdivision of proto- 
stigmata, while the stigmata of the buds arise quite independently ; 
the term “ protostigma ” is new and is given to the transversely elongated 
primary stigmata. It must, of course, be supposed that the larva 
exhibits a more primitive mode than the bud, and the author thinks 
that it may be safely assumed that the protostigmata of Ascidians arose 
primitively in regular order from before backwards. It is very signifi- 
cant that in Pyrosoma the phylogenetic inferences which have been 
drawn from the development of the stigmata in Ascidians are exactly 
fulfilled ; in it the stigmata are arranged in a single longitudinal series 
along each side of the pharynx, and they are transversely elongated, 
from the dorsal surface to the endostyle. They, therefore, resemble 
precisely, both in form and in arrangement, the protostigmata of larval 
Ascidians. The author submits, therefore, that we have in Pyrosoma a 
primitive type of Caducichordate Tunicata, which is antecedent to the 
whole of the phylum Ascidiacea, and which exhibits very closely the 
ancestral form of pharynx from which the complicated respiratory 
organ of the fixed Ascidians has been derived. 
If this view is accepted it will follow that Clavelina and its allies 
must no longer be regarded as the most primitive members of the 
Ascidiacea, and that Botryllus and the Styelinae must take this position. 
Developmental Cycle of Compound Ascidians.f — Dr. J. Hjort finds 
that the whole rudiment of the buds of Botryllidae consists, as in the 
Bryozoa, of two epithelial lamellm of ectodermal origin with mesodermal 
cells scattered in them. From this it follows that the gemmation of 
* Proc. Roy. Soc. Lond., li. (1892) pp. 505 -13. 
f Zool, Auzeig., xv. (1892) pp. 328-32. 
