of the Star 'fishes. 133 



figured larvae exactly resembling those of Sars, and according to 

 his observations the prehensile arms would disappear at last 

 upon the ventral portion. Neither Sars, Desor, nor Agassiz 

 speak of the mouth of the larva ; Busch, however, asserted that 

 he had seen one, between the four prehensile arms ; but this he 

 has given up, since Sars, who has had the opportunity of ob- 

 serving a multitude of larvse, did not see the mouth. 



J. MUller* has minutely observed the larvse of Echinaster 

 sanguinolentiLS ; but, unfortunately, this celebrated naturalist had 

 only spirit-specimens, so that with regard to this point he could 

 obtain no information. Having been unable to procure these 

 larvae^ we are also compelled to pass over this question. Accord- 

 ing to J.Miiller's observations, the prehensile organs are hollow, 

 and have no relation to the digestive organs. In the interior of 

 the body, at the side opposite to the prehensile organs, the sto- 

 mach makes its appearance as a round body with a central cavity. 

 It advances by degrees towards the middle of the body, in pro- 

 portion as the larvse acquire the radiate form. When the sto- 

 mach is completely formed, the mouth opens at the point where 

 it occurs in the adult Star-fish. After these remarks, we shall 

 speak of the development of Pteraster militaris. 



On the 9th of August 1852, we found this Star-fish with 

 young in various stages of development. We know, from the 

 observations of Sars, that the young of E, sanguinolentus and 

 A, Millleri are developed in a cavity situated in the vicinity 

 of the mouth, and which is formed by the Star-fish drawing 

 up its disk, collecting together the widest parts of its rays, 

 and adhering by their tips. In Pteraster militar-is there is a 

 large hollow space between the skin, which bears the calcareous 

 network and the spines, and the delicate soft membrane, which 

 is supported and sustained by the spines, like a roof with nu- 

 merous rows of pillars. At the middle of the back, this mem- 

 brane has a large opening, which is pushed out like the neck of 

 a bottle and surrounded by five small bundles of perfectly straight 

 bristles. At the bottom, just at the middle of this, the anus 

 opens. In the cavity above described the eggs are developed, 

 and the young remain there until they have acquired the radiate 

 form. It is only then that they pierce through the membrane 

 above mentioned. 



The number of young found in the cavity varies : in some 

 specimens we have only found 8-10, in others 20, or even more. 

 Most of the young occur along the arms, and only a few at the 

 middle of the disk. The colour was usually yellowish, and most 



* Ueber den Allgemeinen Plan iu der Entwickelung der Echinodermen. 

 Berhn, 1853. 



