Crustacea. 



6569 



-Zoe, as it appears when 

 just free from the egg. 



is the first stage and Me galop a the second, and both are the young of 

 the same animal. 



That which was received with so much caution is now a well-known 

 fact, nor was the scepticism with which it was received devoid of ad- 

 vantage ; it led to a more extended investigation of the subject, and it 

 has since been proved that the Zoe form of larva belongs only to one 

 order of marine Crustacea; those which are freshwater or land carry 

 their young until they have arrived to a form closely approximating 

 that of the parent. But the Zoe that we take in the open water has 

 much altered, both in form and size, from that of the larva as it quits 

 the egg of the parent. As we see them first they 

 are scarcely a line in length, and closed up within 

 a membrane that conforms to each member and 

 confines every hair, as shown in fig. 1. This 

 tunic is thrown off within a few hours, and then 

 the animal assumes the grotesque form of the 

 recognised Zoe ; it has one horn upon its back, 

 and another projecting forwards in front of the 

 head : these were confined down within the pre- FlG ' ] - 

 vious tunic, but became extended as soon as they 

 were freed. The tail also, instead of being truncated and short, ter- 

 minates in two long styliform processes; these were previously con- 

 tracted within themselves, similarly to the 

 horns upon the back and head, — that is, folded 

 as a telescope is drawn within itself. These 

 extend when the tunic is thrown off. All the 

 hairs are liberated, and the animal appears to 

 have more control over its motions. Previously 

 it appeared, when in the water, to progress 

 spirally ; its big head led the way, but the tail 

 was curved beneath with little power of action, 

 and thus steered the young creature round and 

 round in the direction of its progress. But when the larva is liberated 

 from the embryonic tunic it immediately increases in size, and exhibits 

 a more energetic character; it advances with a jerking motion, and 

 always swims towards the light, keeping near the surface of the water ; 

 probably in the free stale this is the case only in fine weather; when 

 storms prevail and the winds tear up the waters, they sink to rest 

 in the quiet depths of the ocean, where most of them become the prey 

 offish and other hungry Carnivora. We say most of them, for we can 

 hardly believe but. that if all that were hatched were permitted to grow 



Fig. 2— Telson, one half in the 

 other partially freed from tunic. 



XVII. 



2h 



