28 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of one type into another. So the kalymmocytes may be fairly called 
abortive ova. In Salpa, the blastomeres seem to act as centres of 
attraction for the kalymmocytes, regulating the disposition of the latter 
in the upbuilding of the body. From the facts of development, 
Salensky concludes that the Pyrosomidse are derived from Synascidian 
types, and the Salpidte from Pyrosoma - like ancestors. In Pyrosoma, 
the blastomeres and the kalymmocytes share equally in forming the 
embryo ; in Salpa the kalymmocytes are the chief constructive elements. 
Since the embryo developes rather from the ovary than from an ovum, 
Salensky calls the development “ oeiogenesis.” 
In the history of the mesoderm there is alternate construction and 
disruption : the coelom-sacs break up into free mesenchyme cells 
which are again collected. The mesoderm of the cyathozoid may be 
regarded as primitive, which suggests that the ancestors of Pyrosomidte 
were enterocoelic. 
In regard to the whole life-history, Salensky believes that the 
metagenesis of Salpidm and Pyrosomidm is incipient in Synascidians ; 
that the nurse-generation of the metagenetic Tunicates has arisen 
from a precocious budding of the larval form ; that in the first stages 
of the phylogeny the sexual generation was able to reproduce asexu- 
ally (Pyrosomidte) ; and that in the course of further differentiation the 
sexual generation lost this power of budding. 
B. Bryozoa. 
Budding in Paludicella and other Bryozoa.* — The following is a 
summary of the conclusions to which Mr. C. B. Davenport has been led 
by his own studies, and by the results of other investigators. All 
Ectoprocta build stocks or corms, the individuals in which are arranged 
in rows radiating from a centre, and are placed one in front of another. 
New" rows or branches are constantly being produced peripherally, and 
there is no dichotomy in the branching. The body-wall and polypides 
of the median or ancestral branch, as well as the furculations of the 
lateral branches, arise from a pre-existing mass of embryonic tissue — 
the gemmiparous mass. This ha6 a central position, as in the Phylac- 
tolcemata, or a peripheral, as in the Gymnolcemata. 
The outer layer of the body-wall in the budding region is one of 
rapidly assimilating and rapidly dividing tissue ; the inner layer 
becomes filled with food taken from the body-cavity in forms in which 
the latter is early cut off by a partition, but it shows no tendency to 
do so in those forms in which there is a coenocoel. The first impulse to 
the formation of the polypide is found in the outer layer of the body- 
wall (except when this is highly modified, as in Cristatella'), and many 
cells seem to be involved in its formation from the beginning. This 
outer layer is embryonic tissue derived from the tip of the stock (Gymno- 
lcemata), or from the neck of pre-existing polypides (Phylactolcemata). 
It is the direct descendant of the gemmiparous tissue of the larva ; the 
inner layer is also embryonic in the budding region, for in Phylacto- 
loemata, at any rate, the ova arise near the neck of the polypide. The 
outer mural layer becomes the inner bud layer by invagination, with or 
Bull. Mus. Comp. Zool., xxii. (1891) pp. 1-114 (12 pis.). 
