302 



HYDROID^. 



Part IV. 



Fig. 40. 



S 'ff 



Section through the reproduc- 

 tive hydra of Clytia (Ortho- 

 pyxis) PoTERiuM. Drawn by 

 H. J. Clark. 



ci c2 f3 branches of the compound axis 

 of the reproductive hydra. — c* c5 

 wall of hydra. — e ( radiating tubes. 

 — // blind sacs of radiating tubes. 

 — g g furrows dividing the repro- 

 ductive mass. — I spermatic mass. — 

 k the calycle. — /3 outer wall. — 

 ■y inner wall of the medusa. 



various walls and channels of the reproductive calycle. In this wood-cut {F/ff. 

 40), the branches of the compound axis, extending from base to summit, are 



represented by simple rings (c\ c^, c^) around the medusa 

 (/■? y), and the chymiferous tubes of the latter [e e), with 

 their blind sacs, appear furcate. 



At maturity the medusa fills the calycle from base to 

 top (PI. XXIX. Fiffs. 3 and 4, i), while the axis occupies 

 but a small space, being crowded to one side and com- 

 pressed by its swelling progeny. Under such conditions 

 the channels of the axes are collapsed, and the walls appear 

 like wrinkled bands {Fiffs. 3 and 4, c c^), running longitu- 

 dinally over the medusa. So great is the pressure caused 

 by the enormous swelling of the medusa, that, oftentimes, 

 when the calycle opens to allow the egress of the jDlanulse, 

 they are forced out in a body (PI. XXVIII. Fiff. 16, i^), 

 carrying along with them the actinal end of the medusa. 

 In this way there is produced the semblance of an exterior 

 development of a medusa, even to the formation of radiating tubes (e^). The exit 

 of the planulaj is made through an opening between the ends of the compound 

 axes, so that the latter has the appearance of an exterior medusa. This similitude 

 is more fully carried out in the male (PI. XXIX. Fiff. 5), where the medusa {h) 

 opens at its end, and the spermatic mass {i P) streams out through the central 

 aperture (d^) of the disk-like, common termination of the channelled axes; and the 

 latter, at the same time, gradually contract toward the base of the calycle as the 

 mass of the medusa grows smaller. The planules are finally released by the 

 disintegration of the medusa, and they commence an independent life as oval, or 

 more or less ovate solid bodies (PI. XXVIII. Fiffs. 17 and 17"), and move about by 

 means of vibratile cilia, with which they are covered. The planula is not a 

 homogeneous body at this time ; but consists of a very thick outer wall {Fi(/. 17), 

 which is composed of irregularly round cells {Fi^- 18, A), and a central clearer 

 portion which is made up of much smaller cells {Fi(/. 18, B), that appear like mere 

 granules beside those of the outer wall. In an end view {Fi(/. 17"^) of the planula 

 it appears circular. 



A short time before maturity the spermatic particles are broad, flask shaped 

 (PI. XXVin. Fiff. 20, C), and do not possess any filamentary appendage. The 

 fully-developed spermatic particles (Fiff. 20, A B) are elongate, flask shaped, with 

 a moderately long filamentary appendage attached to the broader end. 



Proles hijdroidea. — In the development of the hydra, by the budding process, 

 the proportionate growth of the walls, the mode of formation of the tentacles, 



