374 M. F. E. Schulze on the Relationship 



with the remark that the histological difference between 

 Hydra and Actinia is hardly less considerable than that 

 between Hydra and Spongia. 



These ideas of Leuckart's, which were accepted as essen- 

 tially correct by Micklucho-Maclay, Hiickel, and most spon- 

 giologists, have quite recently been carried further by 

 Marshall *, who has at the same time sought to controvert 

 the arguments which had in the meantime been brought 

 forward by Balfour in favour of the independent origin of the 

 Sponges from the Protozoa. 



While Balfour, in his ' Comparative Embryology ' (vol. ii. 

 p. 285), had cited the peculiar character of the digestive 

 canal-system of the Sponges, in contradistinction to the 

 gastro-vascular apparatus of the Ccelenterata, Marshall, like 

 Leuckart, finds precisely in the agreement of this system in 

 the two groups a principal reason for uniting them in the 

 same type. After appealing to his own observation of a 

 radial arrangement of the first flagellate chambers as diver- 

 ticula of the central gastral space, and to the not unfrequent 

 occurrence of radial symmetry in mature sponges of different 

 sections, he says in conclusion : — " The two groups are Meta- 

 zoa with gastral spaces, mesenterial sacs (which in Sponges 

 may become flagellate chambers), and canals originating from 

 the gastral space and running centrifugally, which open out- 

 wards by means of pores, and (occasionally even in the higher 

 Ccelenterata) serve for the reception of nourishment. These 

 canals, like the gastral spaces (in Renierd), are lined with 

 endoderm, which in both differentiates flagellate cells." 



Balfour had remarked that the early development of the 

 mesoderm in the Sponges stands in striking opposition to the 

 deficiency of this layer in the embryos of most Ccelenterata, 

 and called attention to the remarkable peculiarity of the 

 sponge-larvae. 



Marshall, however, ascribes no pliylogenetic significance 

 to the early development of the mesoderm in the Sponges, 

 referring it to " abridged inheritance," and in general 

 recognizes no important difference between the larvee of 

 Sponges and Ccelenterata. 



The entire absence of urticating capsules in the Sponges 

 is explained by Marshall by their correlative connexion with 

 the tentacles, which the Sponges have either never possessed 

 or lost very early, while they occurred in the true Ccelen- 



• Zeitschr. fur wiss. Zool. Bd. xxxvii. (1882), p. 221 ; and Abhandl. 

 der Berl. Akad. der Wiss. (1884). 



