40 



PROF. AGASSIZ 7 S 



really a longitudinal fissure with lateral folds. All 

 the tentacles terminate with a hole ; they also con- 

 stitute muscular tubes, with longitudinal and cir- 

 cular fibres, by the contraction of which they are 

 alternately drawn in and out. The stomach, like 

 the tentacles, empties into the main cavity of the 

 body (Plnte XXXII, fig. B), so that when the Acti- 

 niae swallows its food, the results of the digestion 

 are thrown into this common cavity, and there 

 circulates by the agency of vibrating cilia between 

 the partitions and in the hollow tentacles, until 

 absorbed by the surfaces in contact. You see, also, 

 in that diagram, that water can be introduced into 

 the inner cavity through the mouth and the stom- 

 ach, as well as through every tentacle, and also 

 thrown out through stomach and mouth, and 

 through every tentacle. The body is thus swollen 

 by the water pumped through the suckers, or by 

 that swallowed through the mouth. When the ani- 

 mal re-opens its mouth to throw out water, the un- 

 digested remains of the food are also expelled. 



When the animal comes out from its contracted 

 position, we see the suckers gradually expanding, 

 (Plate XX, fig. E) and these numerous tentacles 

 pumping water, and the animal successively swell- 

 ing into its various movable changing forms. The 

 existence of eyes in Polypi has been mentioned by 

 Mr. Quartrefages. I have observed them in a new 

 species of Lucernaria discovered upon the beach 

 at Chelsea. In addition to these structures there 

 is hanging from the partitions of the main cavity, 

 [Plate XXXII. fig, B.} below the stomach, a series 

 of bunches of eggs ovaries, below those lower 

 muscular partitions. All Polypi seem to have a 

 structure similar to this. Those which do not re- 

 semble these in structure, are the types which I 

 consider not to belong strictly to the class of Poly- 

 pi. When the eggs of Actiniae are matured, they 

 are let out through the moath. I have had an op- 

 portunity to see this myself. These bunches of 

 eggs are freed in the main cavity of the body, and 

 then through the lower opening of the stomach 

 pressed into that cavity and finally discharged from 

 the mouth, as represented in. this figure. fPlate 

 XXXIII. fig. A.] 



They are sometimes entangled in the cavities of 

 the tentacles, and have even been reported by Sir 

 John Dalyell to be discharged from the tentacles. 

 The young egg of the Actinia presents the struc- 

 ture which we observe universally throughout the 

 whole animal kingdom. They consist of a mass of 

 yolk substance, enclosed in a special membrane 

 {Plate XXXIII, fig. B}. Within is a germinative 

 vesicle, and in the centre a germinative dot (fig. C). 

 These yolks will grow (fig. D), the germinative ve- 

 sicles and dots will disappear, and the germ being 

 formed in the shape of spheroidal bodies, with a 

 darker mass in the centre, will be hatched, and form 

 a more elongated body, (fig. E> the yolk being 

 more distinctly separated from the animal layer 

 proper, which is the external crust of the germ. 

 Above, a depression is formed; the lower part 



is attached upon the soil, and around the sppor 

 depression, (Plate XXXIII, fis F.) there are little 

 protuberances formed, (Fig. G.) the central depres- 

 sion growing deeper, and the mouth is finally pro- 

 duced, surrounded by tentacles. (Fig. H,) Bat the 

 most remarkable feature which I have observed in 

 this development, is that the young Actinia differ 

 from the old ones, in having at first only a few ex- 

 ternal tentacles \ and these few are arranged in a 

 very peculiar manner* Suppose this to be the 

 first indication of the mouth ; there will soon be 

 surrounding tentacles, (Plate XXXIII., fig. H.) at 

 first only five, though ia the full grown animal 

 there will be hundreds. Next there will be others, 

 coming out between the first ones, so that soon 

 ten are formed. Then there are everywhere in the 

 intervening spaces more coming out, so that twen- 

 ty will occur ; and in this way the number is grad- 

 ually increased. But the position of the primitive 

 five ones has a relation to the longitudinal form of 

 the mouth; one of the five primitive ones being- 

 always in the same diameter of the animal as the 

 longitudinal fissure of the mouth. (Plate XXXIIL 

 fig. A.) But the other four are in pairs. 



After I had made this observation, I asked Mr 

 Dana whether he had observed such a symmetry 

 in the arrangement of the tentacles. He stated 

 that he had ; and that in addition, one of the tenta- 

 cles was sometimes different in color from the oth- 

 ers. What this means I shall soon show when 

 comparing the Polypi with the other radiated an- 

 imals. 



But now there are other Polypi whose embryol- 

 ogy has been extensively studied. I mean the Co- 

 rynse (Plate XX., fig. C.) Syncorynae (Fig. A.) and 

 Podocorynse, (Fig. B.) upon which Loven. Sars 

 Steerstrup, R. Wagner, and others, hare made 

 most remarkable observations. And also the Cam- 

 panularia Tubularia, upon which we are indebted 

 to Loven and Von Bereden, and others, for exten- 

 sive information. The Coryne, and alike types are 

 so closely related to the Tubularise, that the resem- 

 blance has been particularly noticed. And this close 

 resemblance alluded to as a sufficient ground to- 

 leave the club-shaped Polypi with Medusa like buds 

 among Polypi, notwithstanding the great differ- 

 ence which has been noticed, both in their struc- 

 ture and mode of development. 



Here we have the Podocorynse (Plate XX, fig. B), 

 and here (Fig. C) the Syncorynse, which are small 

 PolypL The existence in Boston harbor of simi- 

 lar Polypi of the genus Corynse, first described 

 from the Northern shores of Europe, I have as- 

 certained last year, and indeed there is a vast field 

 to explore on these shores, as during a cruise on 

 the South Shoals with Capt. Davis, in 1847, 1 have 

 ascertained the existence of not less than seven- 

 teen species of this family, among which there are 

 types of new genera, which I shall describe oc 

 another occasion. From the upper part of the 

 stem of these Corynoid Polypes there are hanging 

 down several little bell-shaped bodies, of a quad- 



