373 



when the conditions of their life were equally, if not more ob- 

 scure. Siebold, however, has shown that here, although the 

 path taken by Nature is circuitous and intricate, yet, after all, no 

 new features of a heterogeneous nature are introduced, and that 

 all required for the observer is patience and care. It does not 

 seem to me any more improbable that this MoUusk should have 

 entered, in some of its stages, the body of the Synapta, than that 

 the anomalous forms of many Helminths should pursue a like 

 course with the animals in which they are found, as we now 

 know to be really the case. In Muller's last account of the sub- 

 ject, he discusses to some extent these facts. After some re- 

 marks upon the importance of a careful study of the embryology 

 of this form, he says : — "I do not give up the hope that we may 

 yet determine, at least, the germs of this Mollusk, and I found this 

 hope mainly upon the very characteristic form of the spermatic 



particles, beside the other features above mentioned 



The spermatic particles of Natica, and its allied forms, are yet 



unknown In studies bearing upon this matter, one 



should particularly bear in mind the terminal enlargement of the 

 spermatic particles, which, up to this time, has been observed in 

 no Gasteropoda, but which, in the spermatic particles of the 

 Mollusk in question, is never wanting." 



Although for some time familiar with the details of the sper- 

 matic particle of the Gasteropoda, yet, I have very recently re- 

 examined the spermatic particles of Nalica (N. heros) with 

 reference to this point. They resemble closely those of the 

 pulmonary Gasteropoda (Helix, for instance,) and consist of a 

 well-defined cork-screw head, to which is attached a very deli- 

 cate tail ; they agree, in general, therefore, with the form given 

 by Miiller of those of the Mollusk in question. 



Dr. Gould remarked that the shell alluded to probably had no 

 affinity to Natica, but was one of the well-known parasites of the 

 Radiata, especially of the Holothurise, known under the names of 

 Stylina, Stylifer, Eulima, the former of which resembles, in 

 form, a minute Natica. Moreover, he thought it most probable 

 that the animal in which they were found (Synapta digitata) 

 held no relations to the development of this univalve, except to 

 afford it a nidus. 



