COKONATiE NAUSITHOK. 



55.3 



subumbrella; the 4 lips are without prominent oral appendages or palps. The central 

 stomach is connected with a wide annular sinus in the disk by means ot 4 wide, perradial ostia, 

 alternating with which there are 4 short interradial septa (see Claus, 1883, p. 27, tat. 7, fig. 48). 

 The broad ring-sinus is interrupted near the bell-margin In i'> septa in the radii ot the mid- 

 axial lines ot the lappets. These sepia are not complete. howe\er, but lease a marginal 

 ring-canal. Thus the 16 peripheral stomach-pouches are in the ladii ot the sense-organs and 

 tentacles, and are joined by the marginal ring-canal in the axial line ot each lappet. 



Four groups ot simple, unbranched, gastric cirri are upon the interradial septa ot the 

 central stomach and project centnpetally inward into the central stomach; altogether there 

 are about 28 gastric cirri, about 7 in each group. The 8 adradial gonads occur in the 8 ten- 

 tacular radii and are upon the floor ot the subumbrella in the /.one ot the wide, inner ring- 

 sinus ot the bell. Each gonad is large and globular and consists ot a pocket-like told ot the 

 entoderm of the subumbrella (see Claus, 1883, p. 31). A zone ot well-developed circular 

 muscle-fibers is on the subumbrella between, and centrifugal to, the gonads. Centripetal 

 to this, powerful strands ot" radiating muscle-fibers extend outward to the tentacles and mar- 

 ginal lappets; also, 8 poorly developed strands of radiating muscles extend outward in radial 

 and interradial positions from the base ot the oesophagus to the zone ot circular muscles. 

 The color ot this medusa is quite variable. The gelatinous substance ot the bell is usually 

 translucent-milky, greenish, or light brownish. The gonads are brownish or red or, in the case 

 ot the males, bright yellow. Rosin-colored spots m the ectoderm ot the exumbrella, especially 

 upon the lappets, are due to clusters of small crystals (see Claus, 1883. fig. 44, taf. 6). 



A young ephyra of this species was found by us near Flamingo Key, Bahama Islands, 

 February 9, 1893. It was 2 mm. in diameter, and there were as yet no marginal tentacles 



and only 4 gastric cirri A slightly older ephyra has been figured 

 by Claus, 1883, fig. 48, taf. 7. 



This medusa is a surface form, and is common in the Med- 

 iterranean, Atlantic, Pacific, and Indian Oceans, and in all trop- 

 ical or warm seas. Nausithoe polaris (Naupkanta polaris 

 Fewkes) from the Arctic Ocean, appears to be identical with 

 N. punctata, and if this be true Vanhoffen is right in stating 

 that Nausithoe punctata is found in all oceans. It is abundant 

 in summer at Tortugas, Florida, and in the Bahamas, hut has 

 not been found on the Atlantic coast ot the United States north 

 of the Carolinas. Vanhoffen, 1906, describes a specimen 12 mm. 

 wide from N. lat. 59 39', W. long. 8 49'. 



Ilamann, 1883, studied the development of the ephyra of 

 this species and finds that the gonads first appear as 4 inter- 

 radial entodermal swellings in the subumbrella wall of the 



stomach, at a time when the ephyra has but one gastral filament in each interradius. Later 

 the 4 original gonads divide and migrate so as to become 8 in the adradii of the subumbrella 

 wall of the stomach. The genital products oiiginate in the entoderm and migrate into a gelat- 

 inous space between two la\eis ot entoderm. The spermaries appear as a series of follicles 

 in this space. 



According to Metschnikoff, i8So, who has studied the early development of Naiisitlni,- 

 "mar<;iniitii" I which is apparently identical with Y. f>iin, tnl.i I the egg is citron-yellow, 0.23 

 mm. in diameter, and is laid in mid-day in December; segmentation is total but somewhat 

 unequal, the cells of the vegetative pole being hum St. \ wide, central, cleavage cavity is formed 

 and the gastrula results from imagination at the hinder end of the lat\a. The blastopore 

 then closes over and the entoderm is entirely inclosed by a layer of ciliated ectoderm, and 

 the tree-swimming planula is thus formed. 



The remarkable scyphostoma larva of Nausithoe punctata bears a striking superficial 

 resemblance to a hydroid and it lives commensal within sponges such as Subnit, \c, .Uyv/7/rt, 

 Rcneira, Esperia, etc. It is especially abundant at Trieste and Naples. This hydroid-like 

 larva forms a branching tree-like growth within the bod\ of the sponge, the polvp-mouths 

 and their tentacles projecting out of the oscula of the sponge. The branching, tree-like stock 

 ot the larva is covered with an irregularly annulated, chitinous perisarc, which terminates 

 at a short distance below the zone of tentacles of each polypite. The mouth of the polypite 



FIG. 354. " \aupltanla'' albalrossi, 

 .lit. r M.i.r .in \lrm.\lus.Comp. 

 Zoology at Harvard Collr^c. 



