Chap. VII. EUCOPE DIAPHANA. 



325 



larians, are disposed in a single row around the base of a simple proboscidal 

 actinostome. As an instance of the far-reaching power of the tentacles, by means 

 of their lasso-cells, we would mention having seen an Infusorium, which \vas swim- 

 ming in the vicinity of one of the hydr«?, suddenly stopped in its course, and 

 drawn violently to a tentacle, which rolled around it and conveyed it into the 

 expanded mouth, the other tentacles remaining stationary. The mouth expanded 

 rapidly several times, thus causing an inward current, and then closing, the tentacle 

 was drawn out in close contact with the lips, as if to rub off, or prevent the escape 

 of the Infusorium. The disposition of parts in the reproductive calycle, as far as 

 the hydrarium proper is concerned, is the same as in that of Obelia commissuralis 

 (PI. XXXIV. Fig. 11), but the meduste, at the time they are freed, have twenty- 

 four {Fig. ^.f\ instead of sixteen tentacles, and the reproductive organs {Fig. 9% /\) 

 begin to develop before birth. 



The adult medusa of this species has already been described in my Contributions 

 to the Natural History of the Acalephs of North America, under the name of 

 Thaumantias diaphana. 



Embryologg. — The breeding season of Eucope diaphana is during the spring 

 and summer months, while from December to April, in some years at least, the 

 reproductive calycles are absent; but there would seem to be either some variation 

 as regards time, or else those specimens found along shore, in the deep pools 

 close to low-water mark, are not so fertile as those which live in deeper water, 

 or may be retarded in their growth by the changes of alternating tides. We 

 are led to this belief by the fact that, on the sixteenth of April, 1855, we found 

 some free medusae (PI. XXXIV. Fig. 9^) which were identical, in every respect, 

 with those which were taken from the reproductive calycles in September, 1854. 

 The anatomical details of the medusa and its mode of development are, with one 

 or two exceptions, identical with those of Obelia commissuralis, and, therefore, the 

 illustrations of the latter may serve for the former. The only differences between 

 the two are, that the medusa of Eucope diaphana, while attached to the column of 

 the reproductive calycle, develops twenty-four tentacles at once, and that, at the 

 same time, the ovarian pouches {Fig. 9% /') become so far advanced as to be 

 quite conspicuous, and extend from the base of the actinostome half way to the 

 margin ; while Obelia has only sixteen tentacles at first, and no sexual pouches. 

 The eyes (a) are on the second tentacle from the radiating tubes. 



