ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 469 



nervous organ ; the anterior part of the ectoderm becomes the membrane 

 of the fully formed avicularia. 



Genus Steganoporella.* — Mr. Sidney F. Harmer publishes a revision 

 of this genus, giving the characters of twelve species, with keys for ready 

 identification, and careful descriptions and figures. 



New Histriobdellid.t — Prof. "W. A. Haswell has found an interesting 

 little creature, related to Histriobdella homari, but differing from it in 

 many respects, in the gill-chamber of the Tasmanian crayfish (Asta- 

 copsis tasmanicus). He names his find Stratiodrilus tasmanicus g. etsp. n. 

 In external appearance a notable distinction from Histriobdella is the 

 presence of four pairs of cirri consisting of two segments, and tipped 

 with non-motile sensory cirri. In regard to the nervous system, the 

 nerve-cord appears to be much more distinctly differentiated from the 

 epidermis than in Histriobdella. The ciliated canals of the excretory 

 system extend forwards into the head and backwards to the posterior 

 region of the body, which they are said not to do in Histriobdella. There 

 are also some points of contrast in the female ducts of the two forms. 



As to affinities, the author is of opinion that the Histriobdellidae are 

 derived from the Eotifera. He regards their relation with the Poly- 

 gordiidae as extremely remote, and considers that there is a more obvious 

 relation to Dinophilus, which he regards as an offshoot of the Eotiferan 

 stock which gave rise to the Histriobdellidae. 



Rotatoria. 



Apsilus vorax (Leidy).| — Dr. Reinhard Gast records the sudden 

 appearance of this rare and aberrant Rotifer in an aquarium. Unfor- 

 tunately, the animals speedily disappeared again, but some observations 

 on structure and development were made. The free-swimming period 

 is brief, and is soon followed by the disappearance of the larval eyes 

 and by fixation. After once having fixed itself, the animal is incapable 

 of further locomotion, and cannot re-attach itself if forcibly removed. 

 The " fixing-disc " or " sucker " of other authors proves to be the foot, 

 which is furnished with glands which are the homologues of the cement 

 glands of other Rotifers ; this discovery brings Apsilus nearer to the 

 Flosculariae, to which the genus is undoubtedly related. The various 

 organs and systems of A. vorax are described in detail, and a table of 

 the species is given. 



Echinoderma. 



Protoplasmic Structure of Echinoderm Eggs.§— Prof. E. B. Wilson 

 finds that the cytoplasm of the echinoderm egg is an alveolar structure, 

 as maintained by Biitschli. There is no ground of distinction between 

 this and Reinke's "pseudo-alveolar" structure. Tae " deuteroplasm 

 granules " of molluscan and annelid eggs are to be regarded as enlarged 

 alveoli, the substance of which has undergone specific chemical and 

 physical changes, and has increased in amount. 



The rays of the astral systems (astral rays and spindle-fibres) are 

 actual fibrillae, and not merely the optical sections of lamellar plates. 



* Quart. Joum. Micr. Sci., xliii. (1900) pp. 225-97 (2 pis.). 



t Tom. cit., pp. 299-335 (2 pis.). 



t Zeitsclir. wiss. Zool., lxvii. (1900) pp. 167-214 (2 pis.). 



§ Joum. Morph., Supplement to vol. xv. (1899) 28 pp., 2 pis. 



