104 
NOTES AND MEMORANDA. 
He is fully aware of the fact that Professor Butschli 
examined the development of Paludina (‘Zeitsch. wiss. Zool./ 
vol. xxix) for the express purpose of testing the accuracy of 
my statement, and came to the conclusion that the matter 
was as stated by me. Dr. Rabl is scarcely well advised to 
impugn the correctness of an observation, thus supported, 
without offering illustrative drawings^ showing what it is that 
he has seen in the history of Paludina. 
The formation of the primitive nephridia of the embryo 
Planorbis, by perforated cells, similar to those forming 
the nephridia in adult Lumbricus and Hirudo, is admir- 
ably shown by RabPs sections and drawings. — E. Ray 
Lankester, 
Origin of Sperm and Ova from the Cell-layers of Coelentera. — • 
The researches of the brothers Hertwig (‘ Organismus der 
Medusen/ Jena, 1878) upon the histology of a number of 
Medusae belonging to the group known as Hydromedusae led 
them to the conclusion that, uniformly in Medusae of that 
group, the genital products are derived from the Ectoderm. 
This conclusion, corresponding with that of Kleinenberg 
relative to Hydra, led the Hertwigs to consider it pro- 
bable that the observations of Ed^ van Beneden, Ciamician, 
and others, which attributed the ova, or, in some cases, the 
sperm to Endoderm in the sporosacs of certain hydroid 
polyps, were erroneous, and that the derivation of the ova 
and sperm from Ectoderm might be considered as general for 
all the Hydrozoa. 
Claus, however, found the spermatozoa of the medusa 
Chrysaora developing directly from cells of the Endoderm 
over a large surface of the gastric pouches (Polypen und 
Quallen der Adria, ‘ Wiener Denkschr.,^ 1878), and now it 
appears, from further researches of the Hertwigs, upon 
Lucernaria, Pelagia, and Charybdoea (‘ Jen. Zeitschr.,’ 
vol. xiii, 1879), that in the Medusae of the Lucernarian type 
(Acraspedae of Gegenbaur, or better called Scyphomedusae, 
as opposed to Hydromedusae), the ova as well as the sper- 
matozoa uniformly take their origin from cells of the Endo- 
derm. This being the case it seems quite possible that, 
after all, both the observations of Ed. van Beneden and those 
of Ciamician may be accurate, and that in the Hydrozoa 
there is no absolute uniformity as to the origin of the gene- 
rative products. This, however, is not the view taken by 
the Hertwigs. They have extended their observations to 
certain — a very limited selection — of the Anthozoa, and find 
that in them (various Actiniae, Cerianthus, and Alcyonium) 
