66 



INVERTEBRATE ANIMALS. 



Hydrozoa. The special elements of reproduction are developed in 

 these detached buds, but the resulting embryos are not developed 

 into Medusce, such as produce the ova and speim-cells, but straight- 

 way grow up into the plant- like sexless colony, from which the 

 medusiform gonophores were originally budded forth. In these 

 cases, therefore, the individual Hydroid consists of a fixed, rooted 

 colony (or trophosome), producing fresh zooids by a process of bud- 

 ding, but incapable of producing the essential elements of reproduc- 

 tion, together with a free and independent series of generative buds 

 (or gonosome), in which the elements of reproduction are developed. 



Order III. Sbrtularida. 



In this order of the Hydroida we have the most familiar and 

 best known of all our zoophytes — namely, the Sea-firs and their 

 allies. The horny plant -like polyparies of the Sertularida are 



Fig, 34. — a Sertvlaria (Diphasia) pinnata, natural size; a' Fragment of the same en- 

 larged, carrying a male capsule (o), and showing the hydrothecai (A) ; & Fragment 

 of Cavipanuhiria neglecta (after Hincics), showing the polypites contained in their 

 hydrothecse (h), and also the point at which the coenosarc communicates with the 

 stomach of the polypite (c). 



familiar to every visitor at the sea-side, and by those unacquainted 

 with their true nature they are almost universally set down as sea- 

 weeds. The Sertularida are very closely allied to the compound 

 forms of the Corynida, resembling them in being rooted, plant-like 

 colonies, composed of a number of similar polypites or zooids, pro- 

 duced by budding from a primitive zooid. As in the Tubularians 



