ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 591 



bodies, by a structureless tunica adventiva, and by a nucleated tunica 

 propria, which with its internal prolongations divides the gland into 

 spherical segments. The spermatocysts within, surrounded by a 

 nucleated envelope, contain the spermatocytes, and resulting sperma- 

 tides. The investigation of the development of the spermatocytes, 

 preserved in an indifferent fluid, was best achieved by staining with 

 dahlia. The nucleolus both in spermatocyte and sperniatide 

 is described as a thickened inward projection of the nuclear 

 membrane. The nuclear metamorphosis of the probably three 

 successive generations of spermatocytes is described in some detail, 

 and in essential agreement with the accounts of similar processes 

 given by Butschli and Mayzel. The origin of the accessory nuclear 

 body from the cytomicrosomata in the spermatocytes, and of these 

 from remnants of the spindle-fibres is described. As in his previous 

 communications, v. la Valette St. George refers the transitory head of 

 the sperm to the nucleus of the sperniatide, the tail to the proto- 

 plasm, and the middle portion to the accessory body or " Nebenkern." 



Germinal Layers in Hydrophilus.* — Dr. K. Heider has communi- 

 cated some of the results of his studies on the development of Hydro- 

 •philus in an account of the formation of the germinal layers. 



After describing the general characters of the ovum, he notes (a) the 

 appearance, multiplication, and migration outwards of the cellular 

 corpuscles which form the future cells of the blastoderm. These 

 reach the superficial plasma layer, first at the posterior pole, where 

 they become defined into cubical-rounded cells, (b) The next change 

 is the formation of the ventral plate as a somewhat thicker, slightly 

 arched layer, which becomes marked off by longitudinal farrows and 

 slightly projecting lateral walls, to form the endoderm and mesoderm 

 plate described by Kowalevsky. The furrows becoming deeper, 

 unite anteriorly and independently posteriorly, and the whole plate is 

 somewhat sunk below the level of the ectoderm, (c) This is followed 

 by the insinking of the plate, and its curvature into a median canal 

 which becomes grown over by the ectodermic margins. The margins 

 of the furrow-like invagination represent the blastopore, and it is 

 interesting to note that the very anterior portion is the last to be 

 closed, persisting as a distinct aperture in the future position of the 

 oesophageal invagination which occurs at a much later stage. The 

 future closure of this region, and the details of the general invagina- 

 tion, the subsequent broadening and flattening of the tube, as if by 

 dorso-ventral compression, and the appearance of the lumen at various 

 stages till its final disappearance, are then described in detail. 



When (d) the furrow has been completely closed, and when the 

 embryonic envelopes have completely arched over the embryo, Kowa- 

 levsky's second period of development begins, — the period of the 

 differentiation of endoderm and mesoderm, and of the appearance of 

 the organs. On the ectoderm, on both sides of the middle line, 

 the first hint of the nervous system is seen as a slight thickening. 

 The compressed tube, with its all but wholly obliterated lumen, 



* Abb. K. Preuss. Akad. Wiss. Berlin, 1885, pp. 1-47 (2 pis.). 



