ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 741 



surface and is formed by the hinder wall of the sucker. In the succeeding 

 stages the vestibular ring begins to disappear, and the boundaries between 

 its two surfaces are formed by the glandular cells ; at the expense of the 

 pallial surface the tube of the primary zooecium is formed, and at that of 

 the basal the base of the tube. The zocfecium gets the form of a casket, 

 and this the author looks upon as a primary form, regarding the tube as 

 having been phylogenetically acquired later on. The basal side soon 

 gives rise to a lobate outgrowth, which, from its mode of development, 

 appears to be homologous to the stolon of the Vesiculariidte. 



In Crisia, gemmation obtains without the basal wall taking any part 

 in it ; among the Chilostomata the same appears to be true of Bugula. 



The author regards the cephalic amnion-cavity of Sipunculus nudus, as 

 described by Hatschek, as comparable to the mantle-cavity of these 

 Bryozoa. All these strnctures belong to one of two types; there are 

 either two investments which disappear when the animal takes on its 

 definite form, as in Pilidium, or the larval integument alone disappears as 

 in Desor's larva and Sipunculus. In the Bryozoon the investments pass 

 into the organism, where they are used as food. This is the difference 

 between these structures in various worms and in the Bryozoa, and is 

 sufficiently explained by the absence of the functional nutrient tube during 

 metamorphosis. In typical cases (Chilostomata and Cyclostomata), the 

 sucker belongs to the first type, and its thinner anterior wall represents 

 the amnion ; but the mantle belongs to the second type. In the fresh- 

 water Bryozoa the mantle belongs to the first type. 



Development of Alcyonella fungosa.* — Dr. A. Korotneff draws atten- 

 tion to a remarkable peculiarity in the development of Alcyonella fungosa 

 which has not yet been noticed. After the development of a perfectly 

 typical planula there appears a circular fold, which, later on, forms a cap 

 which invests the anterior part of the body. Metschnikoff thought that this 

 cap appeared rather late, while Eeinhard was of opinion that the developing 

 fold appeared before the buds of the polypide. Dr. Korotneff' himself found 

 that the fold might apparently arise either before or after the buds. This 

 difference led to the following discovery ; if the planula possesses two differ- 

 entiated layers, and is of an elongate form, but without buds, there arises 

 around and a little above the middle of the planula, a circular fold, which 

 . consists only of ectoderm, and becomes closely attached to the inner surface 

 of the ooecial sac ; at the point of junction the cells of the inner layer be- 

 come altered in the same way as those of the fold, and there is seen a close 

 circular fusion of the planula with the ooecium ; this line of fusion becomes 

 broader and band-like, and there is thus formed a true zonary placenta. 

 Eeinhard took the commencement of the formation of the placenta for 

 the formation of the cap, but the true cap, as Metschnikoff rightly 

 observed, arises much later ; after the connection of the planula with the 

 osecium is effected, there appear at the upper pole of the planula two buds, 

 which are rightly regarded as finger-like depressions of the wall, and which 

 consist of ectoderm and endoderm. After the appearance of the buds another 

 fold is developed in the middle line, a little below the zonary placenta ; this 

 may be distinguished by consisting of both ecto- and endoderm. As this 

 second fold grows it pushes the placenta upwards; this latter at the same 

 time begins to undergo degeneration — the cell-boundaries begin to disappear, 

 and granules appear in the cells ; the zonary placenta becomes a mass which 

 occupies the whole upper part of the ooecium, and it is possible that the 



* Zool. Anzeig., x. (1SS7) pp. 193-4. 



