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On a Method of Rearing Larvae of Polyzoa. 



By 

 Dr. M. Hasper, Darmstadt. 



Colonies of Bowerhanhia pustulosa, collected in July and August, 1911, 

 in and near Plymouth Sound, contained a great many ovicells and 

 produced numerous larvae, when kept in a flat glass trough and put 

 under circulation during the night. The small yellowish larvae have 

 a decidedly positive phototropism. They gather on the surface of the 

 water on that side which is turned towards the light, from which 

 position they sink to the bottom of the glass. Their movements 

 slacken gradually in the course of a few hours, and at last are limited 

 to revolving in a small circle until they fasten on the sides of the 

 glass. Here they complete their metamorphosis, and in a few days 

 the primary polypides are expanding their ciliated tentacles. The 

 result was better when the just-hatched larvae were brought into a 

 jar sterilised by hot water and filled with so-called outside water, i.e. 

 water from beyond the Breakwater. This jar was fitted with a glass 

 stand carrying a number of cover-glasses. When the larvae settled on 

 these, it was easy to make total preparations of them without detaching 

 them. 



But this method is not sufficient when sections of a just-settled 

 larva or a young primary zooecium are to be made without injuring it 

 by its separation from the substratum. In this case the larvae must 

 be induced to fasten to a material which can easily be cut with the 

 object. For this purpose egg-shells proved useful. They were washed 

 with water, then kept in alcohol of 70 per cent, for about a day, and 

 the coagulated albumen was mechanically removed. The alcohol was 

 afterwards extracted by sea-water. Prepared in this way, the egg- 

 shells were filled with outside water, charged with a number of swim- 

 ming larvae and kept cool by running water underneath an inverted 

 -bell-glass. As long as the larvae were still active, the water was 

 renewed with a pipette twice a day. When the metamorphosis was 

 accomplished and the young polypide began to come out of its cell, it 

 was necessary to add some well-adapted food. I made use of two 

 cultures of algae in sterilised water, kept in stock in the laboratory 

 and kindly placed at my disposal : Fleurococcus mucosus and Nitzschia 



