Chap. I. STRUCTURAL FEATURES. 173 



among Acalephs, in the Ctenophorte generally. I have never observed hermaphro- 

 dites among Echinoderms. 



McCrady has described facts which he considers indicative of a fissiparous mnl- 

 tiplication of the Ctenophorte. What I have seen of the persistence of parts of 

 the body of Ctenophora3 has rather appeared to me as indications of the protracted 

 vitahty of disconnected parts of these animals. When injecting CtenophorcT, I often 

 had occasion to make incisions into their spherosome, and I have always been 

 struck with the power with wdiich these wounds were closed up, by the contraction 

 of the surrounding cells, but never observed a healing process. I have often cut 

 Ctenophoras and other Acalephs into halves, or into smaller segments, without ma- 

 terially interfering, for some time at least, with the manifestations of their vitality. 

 Idyias cut into halves in any direction continued to live in my jars as long as 

 uninjured specimens. I even once saw half of an Idyia close over a small Bolina 

 and digest it, its cut edges overlapping its prey. It seemed to me, sometimes, as if 

 mutilated individuals fared even better in confinement than entire ones. I am certain 

 that this is the case with larger Discophoros. I never succeeded in preserving 

 large specimens of Cyanea entire in my tanks for more than two days ; Init, after 

 cutting off all their long tentacles and their oral appendages and dividing the disk 

 into halves or quarters, I have often preserved such segments for weeks, swimming 

 about as if uninjured, when entire specimens caught at the same time would die 

 and decompose in one or two days. But I never saw the slightest trace of 

 reproduction of lost parts. 



In order to aA'oid the difficulties which, in describing species, might arise from 

 a strict adherence to a nomenclature based upon homologies, it would seem advisable 

 not to use the expression vertical axis or vertical diameter to designate the main 

 axis of the Radiates in general ; for the very obvious reason, that that axis is 

 oblique in a very large number of Echinoderms, as, for instance, in the Spatangoids. 

 I would, therefore, prefer the use of the word actinal axis or actinal diameter, as 

 expressing the axis which unites the actinal and the abactinal poles. The diameter 

 which passes through the longer diameter of the actinostome and corresponds to 

 the lomjiiudinal diameter of the Spatangoids had better be called cccliuc diameter, 

 because it is not, ol^viously, the longest diameter ; though in all Radiates, in Polyps 

 as well as in Acalephs and Echinoderms, it trends in the direction of the digestive 

 cavity, or of the main cavity of the body. The name coeliac, moreover, does not 

 imply the necessity of distinguishing the anterior and posterior ends of a longi- 

 tudinal diameter, which in Acalephs do not differ, as they do in some Echinoderms. 

 For the diameter which, homologically speaking, I have designated as the transverse 

 diameter, I would prefer the name of diacccliac diameter, as it stands in rectangular 

 relation to the coeliac diameter. 



