ZOOLOGY AND BOTANY, MICKOSOOPY, ETC. 571 



the muscular asymmetry, but is of opinion that the latter is the cause of 

 the former. The other longitudinal muscles are the cloacal, of which 

 there are three pairs, and the dorsal and the ventral, of which there are, 

 respectively, one pair. 



Of the transverse muscles, the buccal and cloacal present no remarkable 

 characters ; the branchials are found in the interior of each transverse 

 sinus. The muscular bundle is always single in Glossophorum, which is 

 interesting as being a primitive arrangement, known as yet to obtain only 

 in the Salpidag. The statement of Delia Valle that there are no muscular 

 fibres in the gills of Tunicates is traversed. 



The mesodermic cells, which are elongated, and which give rise to the 

 muscular fibres, have at points along their internal walls refractive thick- 

 enings of contractile substance ; these are developed from the periphery of 

 the cell towards its centre, and so have, in section, a prismatic form. The 

 prisms increase in size till they leave between their faces only an extremely 

 thin layer of protoplasm. The author agrees with Profs. Van Beneden and 

 Julin in thinking that the muscles of adult Tunicates are mesenchymatous 

 in origin and epithelioid in formation. The organogeny of the musculature 

 of the Tunicates appears to be always of one type ; but in the Salpidas and 

 Urodele larvae the mesodermic cells do not elongate. 



The symmetry of the Tunicata, as of the Nematodes and lower Verte- 

 brates, appears to be eutetrapleural and interradial, but this homology is 

 an adaptational and not a primitive one. 



p. Polyzoa. 



Morphology of Bryozoa.* — Herr A. A.. Ostroumoff concludes his study 

 of the morphology of the Bryozoa of the Gulf of Sebastopol. In regard 

 to the metamorphosis of all the three types he notes : — (1) the formation 

 of the basal surface at the expense of the cells of the posterior wall 

 of the vent (ventouse) ; (2) the histolysis of the provisional larval organs, 

 and of the alimentary canal if it be always present (Jlf. zostericola, 

 Cyphonautes) ; (3) the formation of an ectodermic rudiment of the ali- 

 mentary canal, formed by the cells of the cap (calotte) which is invagi- 

 nated (Ctenostomata?) ; (4) the formation on the surface of this rudiment 

 of a mesodermic layer arising from the mesoderm cells of the larva. 



Budding and regeneration are discussed at some length, and the author 

 emphasizes, in conclusion, the following four most important results: — 

 (1) the calcareous skeleton of Bryozoa is deposited between the cells of 

 the ectoderm, which persists throughout the life of the cells as a single 

 layer under the skeleton (in Memhranipora), or as a double layer inclosing 

 the skeleton (in Lepralia) ; (2) the body-cavity is mesenchymatous, without 

 endothelial lining; (3) the vent forms, in Cheilostomata, the basal wall of 

 the cell, aad the stolon in Vesicularia ; on its derivatives the new members 

 of the colony are always budded off, except the opercula avicularia in 

 Cellularia and Escharella ; (4) the polypide is formed at the expense of 

 the ectodermic rudiment and of the brown mass ; the larva still exhibits in 

 its early embryonic life a peculiar organ, known as the cap (calotte), and 

 destined to form the above-mentioned rudiment. 



Morphology of Ectoproctous Bryozoa.f — Dr. W. J. Vigelius, who in 

 1884 suggested that the skin of the adult was represented by the ectocyst, 

 and that the ectodermal epithelial layer which gives rise to the tegumentary 



* Arch. Slav, de Biol , ii. (1886) pp. 32!^-55 fS pis.). 



t Tijdsch. Nederl. Dierk. Vereeii , i. (1887) pp. 77-92 (1 pi.)- 



2 P 2 



