100 MORPHOLOGY. 



direct development, though, as we have already seen, the analogy of the Dlcori/ne gonophore is 

 sufficient to show that no conclusion of the kind can be based on such a character. 



Though the cases thus adduced afford no absolute proof of the direct development of the 

 medusa from the egg, some recent observations leave us no longer in doubt as to the reality of 

 this phenomenon. The observations alluded to have just been made by M. Mecznikoff of St. 

 Petersburgh, who has traced the development of a Cunina as well as that of a Geryonia continu- 

 ously from the egg. In the case of the Cunina, a ciliated planula is immediately developed from 

 the egg, and the planula becomes gradually changed — in a way very similar to that already 

 described by M'Crady — into the form of the medusa. In the Geryonia there is no ciliated 

 planula, and the medusa form is here attained immediately by the development of the ovum.' 



Besides these cases of undoubted development from the egg without the intervention of a 

 hydrifonu trophosome, both of which occur in a group of medusa; of peculiar and exceptional 

 conformation, an instance has been published in which, if the appearances be correctly interpreted, 

 we have in the hydroid medusa of the ordinary type a case of direct development from the ovum. 

 For our knowledge of it we are indebted to Claparede,^ who obtained on the west coast of 

 Scotland a species of Lizzia whose manubrium is described by him as loaded with eggs, some in 

 an early stage, with the germinal vesicle and germinal spot still visible, while others appeared to 

 contain an embryo in various stages of development. Similar ova, with the contained embryo, 

 are stated to have been found floating free in the sea. 



Claparede informs us that the embryo, while still confined within the vitellary membrane, 

 presented all the features of a young medusa : from the centre of the bell-shaped umbrella there 

 depended a thick-walled manubrium, whose cavity extended itself into four radiating gastrovascular 

 canals, which ran in the substance of the umbrella, and opened at the margin into a circular 

 canal, while round the margin were to be seen the rudiments of eight tentacles. Claparede's 

 observation on the development of the embryo did not extend beyond this point ; it is clear, 

 however, that but slight changes were now needed to convert it into the form of the parent 

 Lizzia. 



This observation of Claparede has not been confirmed, and ic is quite possible that the 

 appearances here interpreted as ova in various stages of development are in reality only buds. A 

 very young bud might be easily mistaken for an ovum, and in a medusa, by no means remotely 

 allied to that described by Claparede, buds occur in an exactly similar position, and might easily 

 give rise to an erroneous interpretation of their nature. (See woodcut, fig. 36.) 



' For a knowledge of these facts I am indebted to M. Mecziiikofl', who allowed me not only to 

 inspect his drawings, but to e.xamine his animals iu the progress of their development. M. Mecziiikotf's 

 observations necessitate some modification of a statement made in an earlier part of the present work 

 (see p. 23), and already printed before they came to my knowledge. 



" 'Zeit. fiir wisseu. Zool.,' 1861, p. 401. 



