ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 67 



tubes lying in one plane, from which arise small simple spines and the 

 sessile hydranths, which are of two kinds, nutritive and reproductive ; 

 they are similar to each other and extremely elongate. The nutritive 

 hyuranths may attain a length of two to two and a half centimetres, and 

 bear usually about twenty tentacles arranged in a single circle. The 

 reproductive hydranths are slightly smaller, and bear usually six to ten 

 tentacles, and four or five reproductive buds. Medusa becomes free, 

 though degenerate ; the sexual products are mature wheu the medusa is 

 liberated. The medusa has four radial canals, eight equal rudinieutary 

 tentacle?, mouth-opening and mouth-parts absent, velum developed. 



Pennaria tiarella.* — Mr. M. Smallwood describes the main structural 

 features of this hydroid, and the development of the medusoid. There 

 is in the latter no apparent mouth or circumference-canal. The chy- 

 miferous tubes, which appear by a splitting of four endodermic thicken- 

 ings, entirely degenerate except where the sense-organs occur. Thus 

 the medusoid of Pennaria appears to be in a degenerate condition, and, 

 in a sense, intermediate between free-swimming forms and those which 

 have lost all resemblance to this stage. Cells originating from the ecto- 

 derm, and filling up the cavity between the manubrium and the bell, 

 form the reproductive elements, but only a few of the primitive ova 

 become effective. Many are absorbed by the few successful cells which 

 become mature ova ; others remain simply unused. 



Margelopsis and Nemopsis.t — Dr. C. Hartlaub found, four years 

 ago, an interesting medusoid — Margelopsis haeckelii — -which appeared 

 at Heligoland in great abundance in 1899. It bears on its manubrium 

 numerous " Nemopsis'' polyps (once seen by McCrady in 1857, but 

 never since), which are strikingly Actinula-like. There is no doubt that 

 Margelopsis belongs to the Codonidse, and that the polyps must be placed 

 beside the medusoid-bearing Tubularians. McCrady's polyp, which he 

 referred to a Nemopsis medusoid (N. gibbesii = N. bachei Agassiz), 

 should be ranked as a stage of Margelopsis gibbesii, Hartlaub's M. 

 haeckelii being apparently distinct. 



Fossil Medusae. J — Mr. C. D. Walcott has published a monograph on 

 the known fossil forms and markings referable to Medusae. As a re- 

 viewer notes, " a few years ago no one would have suspected that the 

 rocks of the world could ever yield fossil jelly-fish sufficient in quantity 

 to warrant the publication of a large quarto monograph. Equally un- 

 looked for would have been the fact that the oldest known fauna, the 

 Cambrian, was to furnish a large part of the species, together with a. 

 great abundance of specimens." All the undoubted species are classed 

 with DiscomedusEe, which shows that the differentiation of the Acraspeda 

 must have taken place in pre-Cambrian times. 



Vertical Distribution of Medusae. § — Dr. Otto Maas publishes a brief 

 note on the Medusae of the voyages of the ' Princess Alice.' They in- 

 clude a number of species which are apparently true abyssal forms, and 



* Amer. Nat., xxxiii. (1899) pp. 861-70 (7 fijjs.). 

 t Nachr. Ges. Wiss. Gbttingen, 1899, pp. 219-2-1 (4 figs.). 



I Monographs U.S. Geol. Survey, xxx. (1898) x. and 201 pp. and 47 pis. See 

 Amer. Nat., xxxiii. (1899) pp. 910-1. 



§ Bull. Soc. Zool. France, xxiv. (1899) pp. 165-6. 



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