244 PROFESSOR OSKAR CARLGREN ON THE GENUS PORPONIA 



on each side of the sagittal plane is as follows : 1 (dt.), 2, 1, 4, 3, 5, 3, 4, 1, 2, 1, 4, 3, 

 5, 3, 4, I, 2, 1, 4, 3, 5, 3, 4, 1, 2, 1, 4, 3, 5, 3, 4, 1, 2 = 34 (dt. = directive tentacle). 

 Altogether, therefore, there should be 18 tentacles of the first order, 10 tentacles of the 

 second, 16 of the third, 16 of the fourth, and 8 of the fifth. But it has to be remarked 

 that some groups of tentacles of the first and second orders, namely, the 5 (1, 2, 1, 2, 

 l) in the sagittal plane on both sides of the angles of the mouth, and the 3(1,2, l) on 

 both sides in the transverse plane, arise somewhat further in than the other tentacles 

 of the first and second order. The tentacles of the first order should therefore, perhaps, 

 best be divided into 2 circlets (10 + 8), and similarly those of the second order into 

 2 (6 + 4). The underlined tentacles of the fourth order stand somewhat further out 

 than the others of the fourth order. The arrangement of the tentacles is thus 18 

 (10 + 8) +10 (6 + 4) +16 + 16 (8 + 8) + 8 = 68 (text-fig. 2). As in Halcurias, the 

 peculiar arrangement of the tentacles is connected with a characteristic dislocation of 

 the mesenteries. 



The oral disc is wide, expanded, marked by distinct radial furrows corresponding to 

 the insertions of the mesenteries. The oesophagus is wide, oval, long, and provided 

 with longitudinal furrows to a number of about 18. There are 2 resophageal grooves, 

 lying typically in the angles of the mouth, and broader in the aboral than in the oral 

 part. No hyposulcus is developed. 



Anatomical structure. The ectoderm of the base is high, and consists chiefly of 

 supporting cells, which secrete a fairly thick cuticle. The mesogloea is extensive, as 

 also the entoderm, in which the nervous system seems to be well developed. 



The ectoderm of the body-wall by comparison with the thick mesogloea is thin and 

 provided with numerous spirocysts of varying size up to 60 M long and 11 M broad. 

 Further, there are generally thick-walled capsules (length 26-34 M, breadth 3 M). In 

 cross-section there seem to be thickenings at the base which resemble transversely cut 

 muscles, but are probably in reality thickened basal parts of the ectodermal cells 

 (see below under Ilyanthopsis elegans). The mesogloea is thick, and provided with 

 numerous small cells with outshoots. The entodermal musculature is weak, and no 

 sphincter is present. The entoderm is thin like the ectoderm. The entoderm of the 

 body-wall and of the oesophagus is pigmented. 



The ectoderm of the tentacles is somewhat high, and contains fairly numerous 

 spirocysts and thick-walled nematocysts (length 36-50 M, breadth 3-(5) M). The 

 longitudinal musculature on the outer side of the tentacles is weak, but gradually 

 becomes considerably stronger towards the inner side, so that the muscular wall is here 

 about half the height of the supporting cells. The mesogloea agrees in structure with 

 that of the body-wall. On the inner side, in the lower part of the tentacles, it is, as a 

 rule, just as thick as, or thicker than the ectoderm ; on the outer side, however, it is much 

 thickened (Plate, fig. 6). The thickness decreases towards the tips of the tentacles 

 (Plate, fig. 5), so that at the ends the mesoglrea is almost equally developed round the 

 tentacles. The entoderm is thin, and the ring-musculature weak. The radial muscula- 



(ROY. SOO. EDIN. TRANS., VOL. L., 52.) 



