ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 453 



II. The relation of Monophyidae to DipJiyidge and Pohjplujidae. — In 

 Monophyids, after the formation of the single final bell, there is no 

 further alternation of bells ; the final heteromorphous bell is 

 homologous with the first-formed, heteromorphous, superior bell of 

 the Diphyids. The single, secondary, heteromorphous bell of the 

 Monophyids is final ; in the Diphyids there lies below the two, 

 secondary, heteromorphous bells, a constant reserve supply of 

 similar bells. And if we suppose that the secondary bells of the 

 Diphyids be not thrown off, but, with the growth of young bells, 

 become groups in two similar rows along the stem, then we get the 

 Polyphyid type, as in Hippopodius and Vogtia. 



III. The Eudoxia groups of the Diphyids and their sexual relations. — 

 Under the genus Praya two categories of Diphyids have been included. 

 One, represented by P. maxima, exhibits Eiidoxia~gTO\i])S with the 

 four characteristic constituents, viz. nutritive polyp, tentacle, 

 hydrophyllium, and gonophore. The others, namely, P. diphyes 

 (Vogt and Kolliker), P. medusa (Metschnikoff), and a new form 

 described by Chun, exhibit not only a remarkable multiplication of 

 gonophores with rudimentary umbrellas, but " special swimming 

 bells," with medusiform characters, but without any hint of a 

 manubrium. Prof. Chun proposes to reserve for P. maxima or 

 cymhiformis the generic title Praya, and to erect the genus Lilyopsis 

 for the three others, viz. L. diphyes, L. medusa, and L. rosea. 



Medusae-* — Prof. E. Metschnikoff communicates the systematic 

 results of his developmental study of a number of medusa forms. He 

 describes a Velella medusa, a new species of Tiaropsis, and a number 

 of others, but the bulk of the paper is occupied with purely systematic 

 notes, which do not admit of summary, in regard to a large number 

 of medusoid forms. The communication includes some critical 

 remarks on Hackel's system. 



New Hydroids.f — Prof. G. J. Allman describes a number of new 

 species of Hydroids, chiefly from Australia and the Cape. Theco- 

 cladium is a new genus allied to Thuiaria, but differing in the facts 

 that the branches invariably spring from within the hydrothecae and 

 extend through their orifice ; the habitat of the single species is 

 unknown. Gattya is another new genus, which is intermediate 

 between the typical Eleutheroplean and Statoplean forms of the 

 Plumulariidce ; it has the movable lateral uematophores, and the 

 mesial nematophore completely separated from the wall of the 

 hydrotheca as in the former, and the fixed mesial nematophore and 

 dentate margin to the hydrothecae of the latter ; it is allied to the 

 genus Heteroplon found by the ' Challenger ' ; the habitat of the 

 single species is unknown. Aglaophenia late-carinata sp, n. appears 

 to be a characteristic form of the floating Sargasso-field of the North 

 Atlantic. Thuiaria heteromorpha sp. n. from Tasmania is significant 

 in its bearing on the question of the definiteness of systematic 

 characters, for the form and disposition of the hydrothecas vary in 



* Arbeit. Zool. Inst. Univ. "Wien, vi. (1886) pp. 237-66 (2 pis.), 

 t Journ. Linn. Soc. Lond., xix. (1885) pp. 132-61 (20 pis.). 



