200 HYDROIDyE. Part IV. 



of adherence, comes strongly into profile, and, on this account, the nerve-like appear- 

 ance of its thickness is more apparent than at any other part ; but when the 

 disk is uncontracted, and the innermost wall presses uniformly against the Avhole 

 surface of the middle one, it is possible to observe this same appearance (PI. XIX. 

 Fig. 16, g^) anywhere between these eight points. Looking at the disk from 

 above, the innermost wall, where it bends downwards to l)ecome the outer wall 

 of the proboscis,' resembles, in profile, a quadrangularly-disposed cord (PI. XIX. 

 Fig. 20, c^), surrounding the inner wall {c^) of the proboscis like a nervous ring. 

 At the junction of the transverse partition with the edge of the disk (wood-cut 

 19), the innermost wall bends upon itself at right angles, and there (PI. XIX. 

 Fig. 17, c'), again, when looking across the edge of this angle, its thickness appears 

 like a nervous ring, running along the inner edge of the circular tube. The 

 statement, in my paper on Sarsia, Mem. Amer. Acad, of Sc. and Arts, Vol. IV. pp. 

 246 and 247, that these Acalephs have a specialized nervous system, was based 

 upon these appearances. 



The tentacles are highly developed (PI. XX. Fig. 9), and covered with numerous 

 groups of bristling lasso-cells [h i), admirably adapted to perform the functions for 

 which they are designed. Even at this early period the proboscis has all the 

 flexibility of the adult; this is manifested in a curious way sometimes, by revealing 

 the edge of the mouth so that it doubles upon the superior portion of the pro- 

 boscis for a considerable distance (PI. XX. Fig. 7, a), and then again redoubles in 

 a downward direction {Fig. 7, b), upon the first fold. When the disk is in a 

 contracted state, we may oftentimes see, in a view from above, a remarkable arrange- 

 ment of wrinkles. In the centre, directly over the proboscis, these corrugations 

 form two concentric, quadrilobate rosettes (PI. XVIII. Fig. 18), each lobe being situ- 

 ated directly above a radiating tube. From the end of each lobe two parallel rows 

 of wrinkles proceed about half way down, toward the lower edge of the bell-shaped 

 disk, including, on their way, a deep furrow («), the bottom of Avhich lies close 

 1o the chymiferous tube. Parallel to these wrinkles, two other double rows {b) 

 run from each side of a lobe of the rosette, half way down the disk ; and a double 

 row (c) also starts from the angles between the lobes, and runs outwards in 

 a direction forty-five degrees from the trend of the other rows, and only half as 

 far down the disk. At the lower termination of the rows of wrinkles a band of 

 the same nature runs horizontally around the disk, following all the sinuosities of 

 the umbrella. 



In order to complete the proof that the hydroid form of Coryne mirabilis is 

 the parent of our full-grown Sarsia mirabilis, an attempt was made to rear the young 

 medusae freed from the hydra. In this attempt a partial success was obtained. 

 In six days from the time of birth, the medusae increased from one sixteenth to 



