1875.] On the Locomotor System of Medusa. 143 



in these larvae of Seironota the hinder half of the front notochordal segment 

 is not invested by cartilage. But the hinder, feebly ossified segment has 

 a cartilaginous plate on each side, which is already ossifying (as the ex- 

 occipital), and these ossifying cartilages are seen to be the accurate 

 counterparts of the " neurapophyses" of the first cervical vertebra. 



Afterwards these cartilages grow forward and coalesce with the dorsal 

 ends of the trabeculae. 



These facts are in perfect harmony with what I have been asserting 

 for some years past, namely, that the basioccipital is not the hindermost 

 centrum of a series of cranial vertebrae, but a single bone in the place of a 

 series, the distinctness of which supposed series is lost, their segmenta- 

 tion beiug suppressed. The modified anterior end of the vertebral 

 column forms the occipital arch. There are no developed cranial vertebrae 

 in front of the " epencephalic," which used to figure as the hindermost 

 of four. 



III. "Preliminary Observations on the Locomotor System of 

 Medusse/' By Gr. J. Romanes, M.A., F.L.S. Communicated 

 by Prof. Huxley, Sec.R.S. Received November 1, 1875. 



(Abstract.) 



I. Movements of the Medusce. 

 The movements of some of the Medusae (e. g. Sarsia) appear to be as 

 voluntary as are those of insects. Some of the discophorous species of 

 naked-eyed Medusae*, when threatened with injury, manifest peculiar 

 movements, which are quite distinct from the ordinary locomotor con- 

 tractions. These movements consist in a very strong and protracted 

 systole, followed by a slow and gradual diastole. This spasm-like series 

 of movements is never performed by any Medusa except when the 

 animal is being injured or threatened with injury. 



II. Fundamental Observations. 

 § 1. In the case of all the naked-eyed Medusae which I have this year 

 been able to procure (viz. thirteen species belonging to six of the most 

 divergent genera) I find it to be true that excision of the extreme peri- 

 phery of a nectocalyx is followed by immediate, total, and permanent 

 paralysis of the entire organ. The severed margin, on the other hand, 

 continues its rhythmical contractions as vigorously as when it was still in 

 situ, and this for many hours after the operation. Among hundreds of 

 observations I have only met with one exception to the otherwise uniform 

 result of this operation. The exception occurred in an individual belong- 

 ing to the species Staurophora laciniata. 



* I adhere to Forbes' s classification only because I have not happened to meet with 

 any individuals of the family Lucernariadas. 



