522 NEW YORK STATE MUSEUM 



certain tliat there ^vas intercalated in the multiplication of thecae and 

 growth of the colonies by budding a sexual process of reproduction, and 

 this would be most naturally expected to precede the inception of new 

 colonies, or the formation of the siculae. 



3 The cysts of Diplograptus, in which the siculae are produced, are com- 

 parable in structure and j^^sition to the gonangia or gonothecae of the 

 calyptoblastic Hydroidea, i. e. to the external, chitinous receptacles of these 

 living forms, in which either sporosacs or j)lanoblasts are developed. Both 

 the sporosacs and planoblasts are generative buds, with the difference that 

 the sporosac remains inclosed \vithin the gonangium, giving there origin to 

 the generative elements — ova, or spermatozoa — while the planoblast is a 

 generative bud which is fitted for a free locomotive life and becomes 

 detached from the hydrosome. As the product discharged from the cysts 

 of Diplograptus, the sicula, directly produces new colonies, it can not have 

 been a free generative bud like the planoblast ; and it is hence to be inferred 

 that the generative elements of Diplograptus were produced within the 

 gonangia, and that the ova directly ripened therein into siculae. 



It is true that, in the propagation of Diplograptus by siculae, it has 

 been found that a part of the siculae remains attached to the mother 

 colony, growing out directly into new rhabdosomes, while others are dis- 

 charged with the evident purpose of forming new colonies or synrhabdo- 

 somes. The former might be considered as suggesting, by the retention 

 of their connection with the mother colony, an asexual origin or the nature 

 of buds ; but, theu, it must be considered that the colonial stock or 

 synrhahdosome of Diplograptus is actually a person of a still higher order 

 than a common colonial stock of a hydroid, for it is a colony of colonies, 

 as each " stipe," on account of its origin from a sicula, is homologous Avith 

 the entire colonial stock, or rhahdosome, of a dichograptid or dendroid. 



In the earlier forms, viz the Dendroidea and Graptoloidea Axonolipa, 

 the reproduction may ha^-e been different, in so far as no siculiferous 

 cysts have been found ; and for this reason it is probable that the embryos 

 were discharged at earlier stages. But the final product of the embryonic 



