48 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
notebook kept for the purpose. He has farther made some experiments 
as to the powers of flotation of some of our common seaweeds in water. 
He has had portions of Fucus nodosus floating in vessels of seawater for 
eleven and a half weeks, and F. serratus for upwards of seven weeks. 
He brings forward examples sufficient, he thinks, to demonstrate clearly 
that seaweeds, and particularly those furnished with air-vessels, have 
played in the past, as they continue to do at present, a most important 
part in the dispersal of many of our littoral forms over the globe. 
INVERTEBS.ATA. 
Fecundation, Maturation, and Fertilisation.* — Mr. M. D. Hill 
has notes on the fecundation of the egg of Sjphserechinus granularis and 
on the maturation and fertilisation of the egg of Phallusia mammilata. 
In both he finds there is no egg-astrosphere or egg-centrosome. Both 
these structures are brought into the ovum by the spermatozoa, and they 
give rise by division to all the subsequent astrospheres and centrosomes. 
There is, consequently, no such thing as that which the late Prof. Fol 
called a “ quadrille.” In both the sperm head rotates through 180°, 
and the astrosphere and centrosome are elaborated out of or under the 
influence of the middle piece. In Phallusia the nucleus of the oocyte I. 
contains eight chromosomes irregularly dispersed throughout its sub- 
stance. In the two succeeding nuclear divisions these eight chromosomes 
divide into 16 each time, eight passing out into the first, and eight into 
the second polar body. There is consequently no “ reducing division ” 
at this period. The sperm head breaks off into eight chromosomes, and 
16 are found in the first segmentation spindle. In neither genus is 
there any evidence pointing to the centrosome being an artefact. In the 
former it seems to be all that appears of the middle piece, and is 
brought to light by the disintegration of the latter into granules, and its 
final disappearance. With regard to the relations of the chromatin sub- 
stance during the maturation of the ovum, Phallusia agrees more with 
Vertebrates than with Invertebrates. 
Tunicata. 
New Classification of Tunicata.f — Mr. W. Garstang proposes the 
outlines of a new classification of the Tunicata. He begins by pointing 
out that Herdman’s classification, which is based very largely upon 
modifications of external form, connected with gemmation and the for- 
mation of colonies, involves an unnatural separation of forms which are 
admittedly allied, as well as the unnatural approximation of forms whose 
structure is altogether dissimilar. Mr. Garstang thinks that while 
Lahille’s system, based upon modifications of the structure of the pharynx, 
is admirable for fixed Ascidians, his treatment of the pelagic forms is 
most unsatisfactory. Thus the scheme now suggested by Mr. Garstang 
is based upon anatomical and embryological facts. The pelagic cadu- 
cichordate types possess a single row of undivided branchial slits 
(protostigmata). This condition is recapitulated in the ontogeny of 
various fixed Ascidians, but the protostigmata of the young post-larval 
form are subsequently divided into rows of minute secondary stigmata. 
The group is divided into the Perennichordata and Caducicliordata ; the 
* Quart. Journ. Micr. Sci., xxxviii. (1895) pp. 315-30 (1 pi.). 
f Rep. Brit. Ass., 1895, pp. 718 and 19. 
