521 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
around the yolk-cell in an epibolic fashion. The divisions of these 
blastomeres are in every normal stage approximately synchronous with 
the division of the yolk-cell. The successive cleavages occur in a 
definite and regular order ; in fact, in all important respects, the 
cleavage of L. fascicularis is as regular as that of any other of the 
Metazoa. Previous observers have all failed to recognise any definite 
order in the cleavage of Cirriped ova. There is undoubtedly some irre- 
gularity in the cleavage of the ova of those Cirripeds which have a 
great amount of yolk. The author promises, in a future paper, to point 
out that the cleavage of these forms, when interpreted by that of 
L. fascicularis , follows a much more regular order than has been 
supposed. 
Annulata. 
Fate of the Parent Stock of Autolytus ornatus.*— Mr. P. C. Mensch 
describes a specimen of this Syllid, the study of which leads him to think 
that in this species there is a conversion of a parent stock into a sexual 
individual. Such a conversion of a parent stock has been observed in 
several allies of this form, but in these cases the parent stock acquired 
the characteristics peculiar to the sexual individual. In the author’s 
specimens of A. ornaius no well-marked changes in external appearances 
were observed, and with the exception of a very slight difference in the 
size of the eyes, the ovule-Ior sperm-bearing individuals do not differ ex- 
ternally from those devoid of sexual products. With the exception of 
slight changes of doubtful significance, the internal differences observed 
were no more than such as would naturally result in the displacement 
of the alimentary canal by an accumulation of ovules and sperm-cells in 
the body-cavity. 
Nerilla antennata. f — Mad. Sophie Pereyaslawzewa has studied 
the structure of this remarkable Annelid. It is so remarkable that she 
proposes a distinct family — Nerillidae, with the following diagnosis : — 
The cephalic lobe bears three frontal antennee and two very short lateral 
appendages ; the head is very distinct ; the appendages are undivided, 
aud bear two bundles of simple setm ; all the segments except the 
cephalic have parapodia ; each parapodium has a minute dorsal cirrus : 
there are two long caudal appendages ; the pharynx is simply muscular 
without armature ; the sexes are separate; the female has two ovaries in 
the fourth segment, and two rudimentary seminal vesicles without an 
opening ; the male has much-lobed testes, whence numerous canals lead 
to an ejaculatory duct opening medianly between the third and fourth 
segments. 
The type is represented only by Nerilla antennata 0. Schmidt. Some 
of its characteristics occur separately in other Annelids, e.g. the ciliated 
rings of each segment in the mature animal are also known in Ophryo - 
trocha puerilis, from which, however, Nerilla is very different. Thus, 
while Ophryotrocha is hatched as a trochophore, Nerilla has a direct de- 
velopment. The ciliated rings are not larval, but aj>pear with maturity. 
Another peculiarity is the separation of the two nerve-trunks, which 
have only hints of ganglia and no commissures. It resembles Archi- 
* Zool. Anzeig., xix. (1896) pp. 269-71. 
t Ann. Sci. Nat., i. (1896) pp. 277-315 (3 pis.). 
