802 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
ectodermal thickening may be regarded as the introduction to the forma- 
tion of endoderm. The latter is, of course, so far modified that tho 
immigrating cells must press through the supporting lamella, and the 
old endoderm must be removed. In addition, the ectoderm of the bud 
is no longer histologically indifferent, like the blastoderm, and it is not 
every cell of it which is still sufficiently indifferent to become an 
ectodermal cell. In other points the form of endoderm is the same in 
embryonic development and in budding. The form is known to arise 
by hypotropic (one-sided) or multipolar (all-sided) immigration of 
blastoderm cells. 
If the facts hero related should be shown to have a general signifi- 
cance, the process of gemmation in all Cuidaria, and perhaps in all 
Coelenterata, would be referable to the blastula-stage, or, be regarded 
as derivable from the incomplete division of the blastula. Hitherto, 
gemmation has been regarded as the incomplete division of a completely 
developed form, in consequence of the incorrect view that, from the first, 
both layers took part in forming the bud. 
Metschnikoff has given an account of an incomplete and multiple 
division of the blastula in Oceania armata, and it may be supposed that 
this happens in other forms also. The division of the blastula may, 
again, be regarded as the asexual reproduction of a hypothetical blastula- 
like stem-form of the Coelenterata, which has been atavistically retained 
in the blastula-stage of the latter. 
At first buds could be formed at any poiut of the body of the 
Hydroid, but it was necessary to limit them to definite spots or zones 
in the interest of the formation of regular colonies. 
The mode of budding in Annelids and the strobilation of Scypho- 
polyps and of Cestoda is one in which all the germinal layers of the 
parent take part, and it is quite fair, therefore, to suppose that this 
mode of budding is derived from the capacity for regeneration. 
Porifera. 
Excretion in Sponges.* — Mr. G. Bidder, who has recently suggested 
that the granular cells, which he has called “ Metschnikoff cells,” and 
the glandular ectoderm cells have an excretory function, now gives an 
account of observations which he thinks prove this idea to be correct, 
as far as, at any rate, Ascetta is concerned. After leaving a sponge in a 
solution of indigo-carmine in sea-water he found that the granules which 
are normally present in the Metschnikoff and ectoderm cells become 
replaced by dark-blue granules. The Metschnikoff cells of A. clathrus 
are almost always excavated by a cavity or duct which frequently takes 
the form of a capillary and sometimes branching tube ; they push 
through towards the ectodermal surface, with which they become con- 
nected, and the granular film covering the general gastral surface dis- 
appears. Later on the cells are perforated nearly from end to end, and, 
when they discharge their granules from the external as well as from 
the gastral surface the lumen is completed, and a perforation through 
the wall is formed which, on the regeneration of the gastral epithelium, 
persists as an afferent pore. 
* Proc. Roy. Soc. Lend., li. (1892) pp. 474-81 (4 figs.). 
