514 SUMMABY OF CUKRENT RESEARCHES RELATING TO 



developed in the parts where the ectoderm is deepest. Various forms 

 of capsules for the urticating cells may be developed, and these may 

 be elongated, oviform, pyriform, bean-shaped, or curved, and all kinds 

 of intermediate conditions are to be observed ; connected with these 

 there are various forms of muscialar processes. Closely allied to 

 the urticating-capsule-cells are those which the author distinguishes 

 as flagellate-capsule-cells, which would seem to correspond to that 

 stage of the outer rudiment of the urticating filament (the palpocil- 

 cells) in which the filament has become converted into a flexible con- 

 tinuation of the capsules. Not only can ganglionic cells be always 

 observed, but in some cases {Eudendrmm, Tuhularia) localized aggre- 

 gations of them are to be found at the base of the hydranth, or, as in 

 Campanojjsis, beneath that umbrella-like fold of the ectoderm which 

 is found in the region of the metastome ; and it is important to note 

 that in all these three cases there was a collection of glandular cells 

 just below the ganglionic. No connection between the two could be 

 detected, though there were indications of it in Campanopsis. The 

 author holds to his original view that the ganglionic are derived 

 from those embryonic cells which form a part of Kleinenberg's inter- 

 stitial tissue, and also give rise to the cells of the urticating capsules. 

 Indeed, the author is convinced of the nervous nature of the last- 

 mentioned bodies, and brings forward various facts and considerations 

 to support his view ; in particular we may note his observation that 

 he has repeatedly found an absence of nervous elements in those parts 

 of the ectoderm in which the urticating cells are highly developed ; 

 and we may well believe in the existence of a muscular plexus. 



In the cndoderm we find the ordinary nutrient cells, which are 

 frequently provided with muscular processes. Glandular cells are 

 found most regularly arranged in the region of the hypostome, and 

 are, as a rule, all of one form ; this layer is capable of the most 

 marked changes in form. 



The elements of the " mesoderm " are to be found in all stages of 

 development. The axial cells of the sarcostyle seem to be the least 

 difierentiated from those of the endoderm ; in other cases we observe 

 indications of a localization of the whole tissue, and this is especially 

 seen in the arms. In all the polyps examined it was noted that, when 

 the arms became compressed into one whorl, there was a tendency at 

 the base to the formation of a continuous tissue. These layers can be 

 made out in the supporting lamella, where this is best developed, and 

 of them the median may be regarded as embryonic, the outer as ecto- 

 dermal, and the inner as endodermal. The author enters into some 

 considerations as to the homologies of the arm-like structures, into 

 which our space forbids us following him. 



Development of Hydra.* — A. Korotnefi" has been chiefly studying 

 Hydra aurantiaca, though he has also made some observations on 

 H. fusca. The maturity of the eggs is spoken to by the appearance 

 of two directive corpuscles, which do not seem to owe their origin to 

 the division of a single vesicle, but to be independent formations. 



* Zeitschr. f. Wiss. Zool., xxxvii. (1883) pp. 314-22 (1 pi.). 



