T. B. ROSSETER ON THE GENITAL ORGANS OF TAENIA SLXL'OSA. ST 



The skeleton of the calcareous sponges consists, as is well 

 known, of an aggregation of separate spiculae which are deve- 

 loped exclusively in the ectoderm, and is not, according to Huxley, 

 supported by any framework of animal matter. This statement 

 is equally applicable to the Taenidae, for these spiculae of 

 T. sinuosa, although appearing, when viewed by a 1-in. 

 objective, en masse, yet when they are examined with a \-in. 

 objective and separated by pressure from the globular mass, are 

 seen to be totally distinct from each other. The globulous mass 

 of spiculae is formed between the ectodermal structure or cortical 

 layer and the middle layer. It is easily detached, and then 

 does not carry adhering to it any of the surrounding cellular 

 tissue, thus showing that it is not supported by the same. Thus 

 I look upon this globulous dark point of Dujardin — seeing 

 that it plays no known part in the structural economy of the 

 creature — as a spiculiferous relic, pointing out to us that the 

 Cestoidae are closely allied to the Porifera. This may in 

 some measure explain the views of Yon Siebold as to the 

 calcareous corpuscles which are present in such abundance in 

 the proglottides of some species of Taenia more than in others, 

 being skeletal, and not, as Claparede thought, " the result 

 of an excretion." This affinity is more emphasised and 

 strengthened when we consider and contrast the origin and 

 formation of the spermatozoa and ova in the Porifera and 

 Cestoidae, for the calcareous sponges, like the Cestoidae, are 

 hermaphroditic, and their reproductive elements are spermatozoa 

 and ova ; and whilst it is assumed, for the want of positive 

 evidence, that the former in the calcareous sponges originate in 

 metamorphosed cells in the endoderm, it is a demonstrable fact 

 that such is their origin and development from the endoderm 

 of the middle layer of the proglottis in the Cestoidae, whilst the 

 ciliated embryo of Bothriocepltalus latus, minus its six embryonic 

 hooks, is but the counterpart of that of Ascetta mirahilis. 

 Thus I am inclined to the opinion that the Cestoidae have not 

 undergone retrogression, but that they have always been, in 

 conformity with their environment, as we now find them, 



" anenterous." 



