The early develoi>raeiit of Eudendrium. 259 



The brothers Hertwig (1878) following up their researches upon 

 the histology of the medusae, with investigations upon the origin of 

 the sex-cells, announced that in medusae they were to be found in 

 the epithelium of the sub- umbrella and from a somewhat limited range 

 of comparisons announced the conclusion that among all Hydromedusae 

 the sex-cells arise from the ectoderm and further that among the 

 Scyphmedusae the sex-cells have their origin among the cells of the 

 entoderm, a condition also true for the Anthozoa which had come 

 under observation. 



The extended researches of Weismann (1880, 1881, 1883, 1885) 

 culminating in his classical monograph, 1883, limited almost exclusively 

 to the Hydromedusae, marked apparently the climax of interest so 

 far as it related to this phase of the subject. 



However, investigations have continued with more or less interest 

 up to the present time and not a little revision of Weismann's 

 conclusions has been necessary due in part to the unsatisfactory 

 and inconclusive methods which he had employed in his earlier 

 researches. It should be noted that the work of Weismann had 

 reference, not only to question of fact as to the simple matter of the 

 origin of these cells but as to its bearing upon such problems as the 

 relative rank of the hydroid and medusa, and further concerning its 

 value as a means of classification. 



Weismann has described in considerable detail the origin of the 

 sexual cells in Eudendrium, as has also Kleinenberg, the latter 

 observer, contending for the origin of ova wholly from the ectoderm 

 in contradiction of the former, who allows the possibility in E. capillare 

 of an entodermal origin. Some reference to this apparent contradiction 

 will be made in another connection. 



In a previous contribution (1889), I was led to conclude that in 

 the American species of E. ramosum the ova have their origin in the 

 entoderm. The somewhat emphatic contention of Kleinenberg (1881) 

 to the contrary which later came to my attention, as well as later 

 observations upon these and other hydroids by others led me to a 

 more critical reexamination of my earlier work and its extension to 

 several other species of Eudendrium, namely, E. racemosum Cavolini, 

 E. dispar Agassiz, and a very small species found at Woods Holl, 

 probably E. teuue Ac, also E. capillare, and in brief with the following 

 conclusions: 



1) In E. racemosum Cavolini, ova are undoubtedly found in both 

 ectoderm and entoderm, but the larger were invariably in the e c t o - 



Zool. Jahrb. XX. Abth, f. Morph. 17 



