Echinoderm Larvce uoiih Two Water -Vascular Systems. 325 



hydrocoeles, and these were described in my paper on the development of 

 that species (11). 



In 1910 my friend and colleague, Mr. Fuchs, whilst making cultures of 

 the larvae of Echinus esculenhis, discovered one with two hydrocoeles. This 

 abnormal specimen he was good enough to hand over to me for examination, 

 and in 1911 I published an account of it (14), describing at the same time a 

 similar specimen of the larva of Echinus miliaris, which I had found in my 

 own cultures. In 1911 a larva with two hydrocoeles was observed by 

 Caswell Grave in cultiu^es of the larvae of the Clypeastrid Mellita testudinoia, 

 and a similar larva was found by von Ubisch in 1913 in cultures of the 

 larvae of Strongylocentrotus lividus (18). Finally, in 1914, Gemmill published 

 a description of a number of larvae with two hydrocoeles, which he discovered 

 in his cultures of the larvae of the Asterid Asterias ruhen-s (6). In this 

 paper Gemmill suggests that the doubling of the hydi'ocoele was due to some 

 factor in the environment, because practically all the larvae in one jar 

 showed signs of two hydrocoeles. In 1915 he also recorded the occurrence of 

 larvae with two hydrocoeles in cultures of the larvae of Porania pulvillus (7). 



In this list of recorded instances of the occurrence of two hydrocoeles 

 amongst Echinoderm larvae, it will be noticed that ouly one such specimen 

 was found amongst larvte fished from the open sea, although hundreds of 

 such larvae have been examined. This unique larva was that figured by 

 Johannes Miiller. All the others were found amongst larvae reared in 

 confinement, and this circumstance led me to agree with Gemmill in 

 ascribing the formation of the double hydrocoele to some factor in the 

 environment. Gemmill put forward the tentative suggestion that over- 

 feeding caused the formation of two hydrocoeles amongst Asterid larvae, 

 for he noticed that, in the jar in which the largest number of larvae with 

 two hydrocoeles was found, the diatom {Nitzschia) which he used as food 

 for them had undergone great multiplication. In the process of meta- 

 morphosis amongst Asterid larvae, the partitions between the various 

 ecelomic cavities become to a large extent absorbed, and, in particular, the 

 left posterior ccelom sweeps to the right under the stomach, and opens into 

 the right anterior ccelom. In overfed larvae, according to Gemmill, the 

 swollen stomach prevents this process from taking place, and the right 

 anterior ccelom, freed from the disturbing contact with the left posterior 

 ccelom, develops in the same way as its left antimere, i.e. it buds off a 

 hydrocoele from its hinder end. 



It is worthy of note that Gemmill had previously observed (5) that in 

 about 10 per cent, of the young larvae contained in a normal culture of the 

 larvae of Asterias rubem the right anterior coelom formed a pore-canal, so 



a D 2 



