STUDY OF EYDROZOA. 



r6 



Note. — Stephanocyphus mirabilis AUmau is the type of a new order 

 t>f Hydrozoa called by Allman ThecomeduscB. The animal permeates 

 and is parasitic in sponges. Although a Hydrozoan, it is not a 

 Hydroid, and cannot be referred to any of the existing orders of the 

 Hydrozoa. The ehitinous tubes which permeate the sponge-tissue are 

 united toward the base of the sponge, and constitute a colony of zooids. 

 In many respects it is said to resemble the Campanularim. 



View of the Classification of the Hydrozoa. 



DiaeopTiora. 

 (Anrelia.) 



Siphonophora. 

 (Physalia.) 



Hydrozoa. 



(Hydra.) 



Liibm-at(rry Work. — The common Hydroids, such as Ccrryne, Sertii- 

 iaria, etc., may be collected from seaweeds or the piles of wharves 

 between tide-marks, while the medusae may be obtained by the 

 liandnet, or tow net from a boat. The medusae especially abound 

 -in eddies off points of land where different currents of the sea meet. 

 'Towing is most effectively pursued after sunset and early in the even- 

 ing, when the sea is calm, and the jelly-fish swim near the surface. 

 They should bo placed in the jars by inverting the net in the water of 

 the jar, and examined at once, as many will have perished by the next 

 morning. Jelly-fish can also be reared in roomy aquaria, in which 

 plenty of air is introduced by running water. 



The larger medusae, such as Aureliit, and Gyanea, should be sliced 

 In sections in order to study their gross anatomy, and portions snipped 

 off with scissors to be examined with the microscope. The animals of 

 Sertularians, Coryne, etc., can be studied alive in animalcule-boxes 

 and growing-cells. The coral stock of Millepora was examined by 

 Moseley in groiuid sections. " Portions of the living coral were placed 

 in absolute alcohol, chromic acid, and glycerine ; portions were further 

 treated with osmic acid and transferred to glycerine or absolute alcohol. 

 ^Fragments of the hardened coral were afterward decalcified witli 

 hydrochloric acid, and the residual soft structures were either mounted 

 entire for examination, or cut in the usual manner into fine vertical 

 and horizontal sections, wliich were then stained with carmine or 

 magenta. The specimens hardened in osmic acid, and decalcified after 

 subsequent immersion in absolute alcohol, yielded the best histological 

 results." 



