ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 807 



Porifera. 



Metamorphoses of Oscarella lobularis.* — Dr. K. Heider has 

 investigated the development of Oscarella lobularis O. Schrn. with 

 valuable results. His descriptive memoir is accompanied by sug- 

 gestive theoretical observations. 



After giving an historical summary, Dr. Heider describes (I.) the 

 blastosphere stage. The appearance of the free-swimming larva?, their 

 movements, their occasional attachment, &c, are described, while 

 their histological characters are very fully discussed. The blasto- 

 sphere exhibits a single layer of long, prismatic, ciliated cells round 

 a central cavity which contains non-cellular, granular, albuminous 

 substance. The variations in the ciliated cells in different regions are 

 noted. Each consists of an inner larger portion— the granular endo- 

 plasm, with a store of food-material, and an outer portion — the clear 

 exoplasm with a more definite outer fringe, forming a collar. All 

 the prismatic ciliated cells exhibit a distinctly developed collar. 

 Dr. Heider notes very carefully the intracellular prolongation of the 

 cilium, which is continued within the cell to the neighbourhood of 

 the nucleus. He compares this result with similar observations by 

 numerous investigators. In some cases the root of the flagellum 

 bears on its course, near the base of the collar, a roundish clear 

 body, forming a sort of joint. Besides the flagellate cells, thicker 

 and shorter pear-shaped forms here and there occur. The narrow 

 neck bears a well-developed collar, but no flagellum. It is possible 

 that they may be in some sense secretory. 



II. TJie Gasirula. (a) Free-swimming. — The blastulse become 

 less active, and either come to rest or exhibit only a gentle rotation. 

 They increase in breadth, and invagination occurs generally towards 

 evening. The lower posterior ceils seem to be invaginated. into the 

 anterior, but the reverse seemed an occasional occurrence. The cella 

 retain their characteristics, the primitive body-cavity is still traceable 

 between the two layers after invagination, and the blastopore is seen 

 as a wide circular aperture. 



(b) Attached. — The gastrula fixes itself by the cells round about 

 the blastopore, and pseudopodia are associated with the process. Tho 

 whole larva becomes much broader, more transparent, and more uni- 

 formly coloured. The endoderm cells are not essentially modified, but 

 those of the ectoderm are entirely changed. The collar disappears, and 

 in some cases probably the flagellum also ; the long prismatic form 

 becomes short, and finally cubical ; the difference between exoplasm 

 and endoplasm is no longer demonstrable ; and the nucleus is drawn 

 to the base of the cell. 



(c) Narrowing of blastopore. — The next striking change is the 

 narrowing of the blastopore by an all-round uniform contraction of 

 the margin. A floor is thus made to the gastral cavity. Apart from 

 various changes in external contour, &c, the endoderm exhibits an 

 active progressive growth, and becomes somewhat folded. 



* Arbeit. Zool. lust. Univ. Wien (Claus), vi. (1886) pp. 175-236 (3 pis.). 



