436 NOTES AND MEMORANDA. 



of tlie liiglier animals ; and not a syncytium, that is, composed of fused 

 cell-bodies with imbedded nuclei. 



Both the migratory cells and the collar-bearing cells lining the 

 ciliated chambers contain in their protoplasm yellow pigment granules. 



The sexes are distinct. The spermatozoa have an ovoidal head and 

 a long delicate tail, and occur in definite aggregations, each enclosed in 

 a special cavity of the mesoderm lined by a single layer of flat poly^ 

 gonal cells. Probably, as in Halisarca, each aggregation is formed 

 by the repeated division of a single cell. The ova are contained each 

 in a similar cavity of mesoderm : the vitellus is opaque, owing to the 

 large number of yolk- granules: there is an excentric germinal vesicle 

 and refractive germinal spot. Probably the eggs, like the aggregations 

 of spermatozoa, result from mesodermal leucocytes. 



Only one developmental stage of Aplysilla was observed — the 

 blastula jihase. This consists of an oval body, covered with a single 

 layer of cylinder cells, each provided with a long cilium, and en- 

 closing not, as usual, a clear fluid, but a definite tissue, consisting of 

 stellate cells with anastomosing processes. From this it seems probable 

 that the mesoderm in Aplysilla is formed actually before the gastrula 

 stage. 



The other species of this genus, A. rosea, is remarkable from the fact 

 that it is hermaphrodite, young eggs and sperm-aggregations being 

 found in one and the same section. 



Structure of Spongelia. — In a memoir on this genus of horny 

 sponges, F. E. Schulze * gives, besides an historical summary and 

 enumeration of the species, a full description of Spongelia avara and 

 of S. pallescens, and short accounts of S. elegans and S. sjnnifera. The 

 genus itself is distinguished, according to Schulze's observations, by 

 the following characters. 



1. The possession of large, simple, saccular, ciliated chambers, 

 which are provided with numerous inhalent pores, and possess a wide, 

 round, exhalent aperture, opening directly into one of the efferent 

 canals. 



2. The complete absence of highly refracting granules in the 

 matrix of the connective tissue surrounding the ciliated chambers. 



3. The extensive enclosure of foreign matters by all the chief 

 fibres of the skeleton ; the thin connecting fibres may or may not 

 contain foreign particles. 



4. The more or less uniform development of conical elevations 

 (conuli), 1-8 mm. high, and the same distance from one another, over 

 the whole surface of the sponge, with the exception of the area 

 surrounding the osculum. 



5. avara. — The skeleton in tliis species consists of a network of 

 fibres of spongiolin, in which are imbedded great numbers of foreign 

 bodies, the chief of which are broken spicules of other sponges, both 

 siliceous and calcareous, fragments of plates and spines of Echinoderms, 

 shells of Foraminifera and sometimes of Radiolaria, as well as frag- 

 ments of the hard parts of worms, molluscs, &c., and sand-grains. 



* 'Zcitsch. f. wi.ss. Zool.,' xxxii. (1878) 117. 



