BIOLOGY. 
Tun. 3 
Ascidians. After discussing the general structure, the orientation, the 
body-form, formation of colonies, size and colour, he passes to the com- 
position and chemistry of the test. All important points are, as in the 
preceding parts of this work, very fully and satisfactorily illustrated. 
Bancroft shows that the Pacific species Chelyosoma productum is quite 
distinct from its Atlantic representative C. macleayanum. He describes 
the arrangement of the muscles and the structure of the test, and considers 
the genus closely related to Corella. 
b. Embryology. 
Metcalf supports Brooks’ statement that the blastomeres really build 
up the body eventually, and that the kalymmocytes are merely temporary, 
pass into the bodies of the blastomeres and there undergo degeneration. 
Lefevre points out the conflicting statements as to the origins of 
organs in the buds of compound Ascidians and rightly observes that it is 
desirable that the process should be studied in many other species where 
the bud development has not yet been traced. He has studied the process 
in Ecteinascidia turbinata , Herdman, and finds that bud development 
cannot be harmonised with the germ layer theory. He considers that 
Ecteinascidia differs from Clavelina and agrees with Perophora in the total 
absenco of the epicardium ; but docs not show the rotation of the inner 
vesicle seen in Perophora. The bud begins as two concentric vesicles, 
derived from the stolon, and the development as a whole is very like that 
of Perophora. The inner vesicle is derived directly from the stolon ic 
septum which is not flattened. The pericardium and heart and the dorsal 
tube or hypophysis arise from the wall of the inner vesicle and possibly 
to some extent from free blood cells which have wandered out from the 
wall of the inner vesicle. The primitive inner vesicle is therefore the 
most important part of the bud, and the ectodermic vesicle plays no part 
in the development except the production of the future ectoderm and of 
the test. Even the gonads are derived from the wall of the inner vesicle. 
He finds that free amoeboid blood cells derived from the wall of the inner 
vesicle play a considerable part in forming some organs, such as the 
commencement of the pericardium, and of the dorsal (neural) tube. The 
ganglion is differentiated from the dorsal wall of the neural tube. He 
does not consider the bud development to be at all comparable with the 
embryonic processes. 
Caullery describes the details of the precocious budding of Diploso- 
moides. He shows that after hatching the larva is composed of (1) a 
typical oozooid except that the rectum is atrophied, (2) a typical abdominal 
bud, and (3) two complementary thoracic half buds. This larva is really 
two individuals, the oozooid and the different parts of a blastozooid. He 
explains the separation of the two halves of the thoracic bud by the 
mechanical influence of the abundant yolk. He is unable to confirm 
Lahille’s account of dimorphism in the larva. 
Todaro has worked at the development of Salpa africana-maxima , and 
he now gives an account of the formation of the various organs in the an- 
terior part of the body. In the mesenchyme between the endodermal and 
ectodermal vesicles are formed the peribranchical sac, the cerebral vesicle, 
the pericardium, and it may be reproductive organs. A primitive mouth 
or palcoostome forms which becomes a closed sac. This then opens into 
the anterior brain vesicle (palfeoneural canal) for a time. The subneural 
gland is paired and is derived partly from the corobral infundibulum and 
partly from the ectodermal palseostome. The “ neostome ” forms later as 
a stomodseum. The development and differentiation of the ganglia and of 
the eyes are traced in both the solitary and aggregated forms. 
1897. [Vol. xxxiv.] c 11 
