AVI'lluMI-'.DI'S.K roh KYNK. 



between European and American meiiusiT of Po<locor\rif r,ir'ifti. 



Podocoryne carnea Podocorynr i.irnra 

 Sars, of Europe. var. americana. 



Bunting, the ova originate in the entoderm, Init the sperm originates and remains in the ecto- 

 derm. When the medusa is mature both ova and sperm arc found in the ectoderm of the 

 stomach. In the female, the ova are large and prominent and are spherical in form. The 

 entoderm of the manubrium and of the tentacle-bulbs is red, or brown to red, in color. 



H yJroiJ unJ \oung medusa. No specific difference exists between the American and 

 European hydroid stocks of Podocoryne, The hydroid (plate 14, fig. 2) is commonly found 

 upon shells which are tenanted by the hermit-ciah (I'lignnn) and also upon the carapace of 

 I.imulus. The polypites arise at somewhat irregular intervals from a hydrorhi/.a which clings 

 to the surface of the shell, etc., upon which the stock is growing. In young colonies the hydio- 

 rhiza consists of an open network of anastomosing fibers, which are covered by :i thin, delicate 

 pensarc, and externally by a fleshy hydrocaulus, or ccrnosarc. As the colony becomes older, 

 however, the fibers of the hydrorhiza form a closer network, and the chitinous perisarc fills in 

 the spaces between them. Numerous short, chitinous spines are developed upon the crust 

 which covers the fibers, and thus we find the polypites arising from a fiat, spinous base which 

 adheres to the surface on which the colony is growing. The colony is composed of two kinds 

 of hydranths: sterile feeding-polypites, and reproductive gonostyles. The sterile feeding- 

 polypites are spindle-shaped, being about twice as wide near the oral circlet of tentacles as 

 they are at the base. They have 12 to 16 straight, stiff" tentacles. The mouth is situated at the 

 apex of a dome-shaped proboscis. They are very contractile and may vary in length from about 

 5 to I 5 mm. The reproductive polypites, or gonostyles, are frequently exactly similar in si/.e 

 and shape to the feeding-polypites, and, in tact, are probably merely feeding-polypites which 



have developed medusa-buds 

 (see plate 14, fig. 2, <;). In 

 other instances the gonostyles 



o 



are smaller and more slender, 

 and possess not more than 4 

 to 8 tentacles (see g', fig. 2>. 

 The medusa-buds arise from 

 a zone which is slisrhtlv below 



D 



the circlet of oral tentacles. 

 From 4 to 8 of these buds are 

 usually to be seen upon each 

 gonostyle. According to Mar- 

 tha Bunting, 1894, it appears 

 that the medusa-bud arises as an outpushing of both entoderm and ectoderm of the gonostyle. 

 As the bud progresses in its development, we find the ova in the entoderm of the manu- 

 brium. When a later stage has been reached the}' migrate from the entoderm into the 

 ectoderm. The spermatozoa, on the other hand, originate in the ectoderm of the manu- 

 brium, as was shown by Weismann, 1883. When set free the medusa usually has 8 ten- 

 tacles: 4 radial and 4 interradial. The radial tentacles are usually better developed than the 

 interradial and in some individuals there are but 4 tentacles at the time of liberation, the inter- 

 radial ones not yet being developed. 



It is remarkable that while in some stocks of Podocoryne the medusae are set free in an 

 immature state, in others the medusae are mature when liberated, the manubrium being 

 distended with sperm or ova, which are discharged almost immediately after the medusa is 

 set free. It is possible, as Allman, [871, suggests, that this difference may be due to the influ- 

 ence of local conditions, which may be favorable in the one case and not so in the other to an 

 advanced development of the medusa. Krohn, 1851 , and I. oven, [857, have observed Stocks ol 

 the European form of PvJticnrvni* which were setting ticc mature medus:e. Indeed, we appeal 

 to have a parallel case in Stinm on the Massachusetts coast, where immature medusae are liber- 

 ated during the early spring months, whereas the medusae become ripe, discharge then genital 

 products and wither upon the hydroid stock in May. Good figures of I'lnlmm \n<- stocks which 

 are setting free immature medusae have been given by Sars, 1846; Ilincks. ifsViS; Allman, iX-i; 

 etc. When set free the medusae commonly have 8 tentacles, 4 radial and 4 interradial. The 

 radial tentacles are usually more advanced than the interradial, and in some few individuals 



Number of tentacles when liberated 

 from hvdroul. 



Number of tentacles possessed bv 

 mature medusa. 



Mrilus.i-lnuls on interradi.il suit's i>f 

 stomach of medusa. 



Usually 4 to 8, rarely 

 ih (Graeffe). 



Observed by Sars, 

 1846. 



4 in S. Usually 8. 



16 to 32. I'su.illv 



.iln.ut 24. 



No medusa-buds 

 observed . 



