12 EMBRYOLOGICAL MONOGRAPHS. 
7. Older embryo, in which a ‘horn-like sheath ” (0) (perisare) has formed over the surface of the bud. eb. Epi- 
* blast of hydroid. hb. Hypoblast of the hydroid. i). gm. Hypoblast of bud (?). This may be epiblastie. 
th. Tube in profile. ¢b/. Tube in face. 
8. Older bud, in which hypoblast and epiblast ave well marked. ¢6. Epiblast. id. Hypoblast. The cireular 
canal (can. crc.) is beginning to form by an approximation of two radial chymiferous vessels on each side. 
a}, x?. Infolded outer wall. 0@. Perisare. : 
9. In this bud,-somewhat older than the preceding, the cireular canal (can. eve.) has formed by a coalescence of 
the extremities of the radial tubes. eb. Epiblast. hb. Hypoblast. 7. w. Internal bell wall. m. w. Middle 
bell wall. man. Manubrium. ‘a. Tentacle. 
10. Older bud, in which the circular canal (can. ere.) is fully formed, and a yelum is developed. ¢ b. Epiblast. 
ex. ta, External wall of the tentacle. ex. man. External wall of the manubrium. ez. vel. External wall 
of the velum. 7% man. Internal wall of the manubrium (2). 7. ta. Internal wall of the tentacle. 7. ved. 
Internal wall of the velum. @. Perisare. 
11. Older medusa bud, with tentacles coiled up in the future bell cavity. can. cre. Circular canal. eb, Epiblast. 
ex. man. External wall of the manubrium. ex. ta. External wall of the tentacle. ex. vel. External wall 
of the velum. 7. man. Internal wall of the manubrium. 7. fa. Internal wall of the tentacle. @. Perisare. 
12. A constriction takes place at the point where the medusa bud rises from the hydroid, and the bud is sepa- 
rated from its attachment and swims away. The perisare is ruptured to allow this eseape. Free medusa, 
called Sarsia, which, according to Agassiz, develops from the buds of Coryne (tentacles cut off). fd. Folds 
in the side walls of the bell. man. Manubrium. or. Mouth. tb. Chymiferous tube. oc, Remnant of a 
tube which formerly connected the cavity of the hydroid and that of the manubrium. 
13. Older Sarsia. man. Manubrium ; the upper letters (man.) indicate a bulbous enlargement of the cavity 
of the manubrium where it joins the hydroid. can. erc. Cireular canal. or. Mouth. ta. Tentacles, 
ubr. Umbrella. vel. Velum. 
14. Coryne, showing the relationship of the medusa-buds (future Sarsic) to the tentacles of the hydroid. mds. 
gm. Medusa buds. py. Hydro-polyp axis. py. ta. Polyp tentacles. 
15. The male hydroid ; the almost perfect medusa is persistent, ‘‘ developing the spermatic mass around the pro- 
boscis to an enormous extent,” Agassiz. or. Mouth. py. a. Tentacles of the hydroid. py. s. Stem of 
the polyp. man. Manubrium, “loaded with sperm.” ta. Tentacle. oc. Point of attachment of bud 
(gonophore g) to the hydroid. 
16. A more developed male gonophore, which, according to Agassiz, is persistent, and has discharged the sper- 
matic contents. vel. Infolded velum. . Point of attachment of the umbrella to the hydroid, 
17-23. Hybocodon prolifer, Ag. 
17. A profile view of the head of the hydroid, crowded with medusa buds (mds. gm). py. ta. Peripheral row of 
tentacles. py. ta’. Middle row of tentacles. py. Hydroid axis. 0. Ferule-like enlargement of the perisare. 
X. AA. Bases of tentacles (peripheral). 
18. Head of a hydroid, with the circle of peripheral tentacles (¢a.) cut off. mds. gm. Medusa buds. py. Hydroid 
axis. 6!, Ferule-like enlargement of the perisare. 
18*. Head of the hydroid without medusa buds, showing the position of the two rows of tentacles. py. ta. and 
py. ta’. Tentacles drawn together. 
19. A young bud in earliest condition. 
19°. The same ; somewhat older. ¢6. Epiblast. 6. Hypoblast. 1b. Chymiferous tubes. 
20. A well developed medusa, just before rupturing its connection with the hydroid, and showing the tentacles 
on one side. cav. Bell cavity. can. cre. Circular canal. eb. Upiblast. 4b. Hypoblast. man. Manu- 
brium. man’. Base of manubrium, the eavity of which is somewhat enlarged. mds. gm. Medusa buds. 
The second and third formed buds have begun to appear, and are lettered in order of appearance, — 
2 mds. gm., and 3 mds. gm. ta. Tentacle. ta’. Base*of tentacle not yet enlarged into a bulb. @b. ta. Chy- 
miferous tube in the same spheromere as that to which the tentacle hangs. #8. Tube diametrically oppo- 
site the tentacular tube. 5, Chymiferous tube facing the observer. /0*. Continuation of a chymiferous 
tube into one of the tentacles. £ Enlargement of the tube at the junction of éb* and the circular canal 
(can. cre.). 
20°. A (female ‘) medusa partially developed from the base of the tentacle. cav. Internal cavity. eb. Epiblast. 
hb. Wypoblast.  tb., tb’. Chymiferous tubes in profile and in face. 2 mds. gm. A secondary medusa, bud- 
ding from the walls of the first. The medusa buds represented in the figure are taken from a medusa 
already formed. 
21. View of a medusa older than the last, still attached to the hydroid (seen looking at the inner face of the 
tentacle). cuv, Bell cavity. eb. Epiblast. gm. A small bud, which will probably later develop into a 
tentacle. Ab. Hypoblast. man. Manubrium. man’. Base of manubrium. mds. giu.-3 mds. gm. Medusa 
