588 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
ectolemma, mesolemma, endolemma. All the varied developmental con- 
ditions which control embryogenesis are strikingly different from those 
which obtain during asexual reproduction ; so that the primary embryo- 
genetic processes should be clearly distinguished from the secondary 
ones which prevail during asexual reproduction and regeneration. 
Further, a difference in the origin of the formative cells of an organ 
during embryological development on the one hand, and budding or 
regeneration on the other, does not in any degree vitiate the theory of 
the homology of the germ-layers, or the correlated homology of organs. 
The independence of the two processes is to be explained on “ mechani- 
cal ” grounds, and the germ-layer doctrine is to be regarded as a deduc- 
tion from the observed fact that homologous organs always originate in 
the embryo from cell-layers having the same relative position in the two- 
layered embryo. 
INVERTEBRATA. 
\ 
Fauna of Frog Spawn.* — Herr C. Thon gives an interesting account 
of the animals which he found in ponds in Bohemia associated with the 
spawn of Rana fusca and R. esculenta. In two different localities the 
fauna was almost identical. 
During the first days the spawn remained without associated animals. 
When the spheres of jelly had swollen up, and some of the brood had 
begun to take form, guests appeared. First he observed small Dyticidse : — 
Rydroporus halensis, H. pictus, Haliplus fulvus, Rhantus notatus, which 
were not seen to injure the eggs. For a time before hatching there 
were some water-mites about, Eylais setosa Koenike and Hydryphantes 
ruber De Geer or H. dispar v. Schaub. As the jelly became softer, 
Copepods appeared, e.g. Cyclops languidus Sars and C. fimbriatus Fiscb., 
and rarely a few Cladocera (Chydorus sphsericus, &c). Ostracods seemed 
to help to loosen the jelly, e.g. Cyclocypris laevis and some young forms 
of Cypris reticulata. After hatching, there were many larvae of Clo'eon 
dipterum, Ceratopogon, Chironomus , Limnophilus, &c., and many of the 
insect larvae devoured the young tadpoles. Beneath the spawn there 
was Asellus aquaticus. Nymphs of Curvipes fuscatus and C. conglobatus 
were also common. Among the tadpoles there were individuals of Poly- 
celis nigra. When the empty spheres sank to the bottom, they were 
associated with encysted Vorticellids, numerous monads and diatoms, 
some statoblasts and ephippia, but no Infusorians or Rotifers. 
Mollusca. 
y. Gastropoda. 
Agglutinative Action of Snail’s Albumen Gland. |—L. Camus finds 
that solution or extract of the snail’s albumen gland contains an “ agglu- 
tinin ” which agglutinates diverse substances, such as blood-corpuscles 
and milk-globules. It is possible therefore that the substance of the 
gland may have some agglutinative role in reproduction. 
Function of Gastric Gland in Snail.:]; — W. Biedermann and P. Moritz 
describe the three kinds of cell in this gland, — (u) secretory cells, 
* Yerh. Zool.-bot. Ges. Wien, xlix. (1899) pp. 391-3. 
t Comptes Rendus, cxxix. (1899) pp. 233-4. 
X Arch. f. Physiol., lxxv. (1899) pp. 1-86. See Zool. Centralbl., vi. (1899) pp. 675-6. 
