588 SUMMARY OF CURRENT RESEARCHES RELATING TO 



however, the apical endocyst becomes differentiated into two systems of 

 tissues — the parietal endocyst, which continues to form and thicken and 

 gradually loses its vital structure and activities, and the endosarc, or 

 central endocyst (or funicular tissue, &c), which takes on a special 

 structure varying with different species, but always preserves its vital 

 activity and remains an indifferent tissue. As soon as the homogeneous 

 tissue which forms the polypide has become differentiated into two 

 layers, there is an ectodermal tissue enclosed in a pouch which is at once 

 endoderm and mesoderm. This tissue undergoes a fresh differentia- 

 tion, for in its centre a small mass of cells which will form the intes- 

 tine become isolated. Henceforward the individual bryozoon is con- 

 stituted, and so far the author agrees with Vigelius, Haddon, and 

 Barrois. Before the appearance of the polypide in the zocecium the 

 latter has only contained an indifferent tissue ; after its appearance all 

 is changed, and a number of organs appear. The tentacles with their 

 flagellate epithelial cells, and the epithelium of the lophophore and of 

 the oesophagus no doubt represent the ectoderm. The tentacular sheath 

 consists internally of muscular fibres, and externally of a layer of 

 delicate flattened cells, which appear to be ectodermal. The parietal 

 endocyst, differentiated and specialized as it is in Flustra, may be 

 regarded as forming an outer skin, or somewhat more definite ecto- 

 derm. All the parts in the zocecium, which are contained between 

 the outer skin and the intestinal epithelium with the internal epithe- 

 lium of the tentacular sheath form the mesoderm and the general cavity. 

 In a future work the author hopes to show that in Endoprocta 

 and Lophopoda the endocyst and endosarc take on the special cha- 

 racters of an ectoderm and a meso-endoderm ; that the archenteron 

 arises in the midst of this latter ; that the lophophore, oesophagus, and 

 rectum are directly produced by the ectoderm ; and that in all 

 Bryozoa the polypide is constituted and developed along a general 

 uniform and common plan. 



Development of Cyclostomatous Marine Bryozoa.* — Herr A. 

 Ostroumoff finds that the larvae of the Cyclostomata are the most 

 simply organized of the marine Bryozoa ; their whole surface is covered 

 with cilia ; at one pole there is a sucker, and at the other the mantle- 

 cavity. The endodermal cavity disappears before the larvae escape ; 

 there is no velum, and no other provisional organs are developed. 

 As in other larvae, metamorphosis commences with the protrusion 

 of the sucker which forms the basal wall of the primary zocecium, 

 and with the overlying of the basal surface by the mantle. The 

 broadening basal wall gives off a special kind of stolo prolifer, the 

 " lame germinale " of d'Orbigny. The ectodermal rudiment of the 

 polypide is formed from a plate which is delaminated from the 

 ectodermal cells at the point where, in other larvae, the velum is 

 developed. This plate then bends basalwards and becomes invested 

 by mesodermal cells. The so-called " lame germinale " is homo- 

 logous with the stolo prolifer of the Vesicularidae, and the groups 

 Incrustata and Stolonifera connect therefore the two orders, 

 Cyclostomata and Ctenostomata. 



* Zool. Anzeig., ix. (1886) pp. 283-4. 



