ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 53 



surface of the crab. After it has become fixed it undergoes a mar- 

 vellous metamorphosis, becoming an elongated sac, in which little of 

 the Cypris is left save the outer integument and the spherical mass of 

 cells. A dart-shaped body is now developed at the antennary pole, 

 which is driven into the tissues of the crab ; to this dart the cellular 

 mass is appended, and it, therefore, makes its way into the body of 

 the host. 



The author believes he has shown that all that forms the adult 

 Sacculina arises from the nucleus of the internal Sacxulina, and that 

 the basal membrane with its tubes arises from the sac which con- 

 tained it. The wall of this sac represents the integument of the 

 NaupUus or Cypris, and the nucleus the cellular mass contained in its 

 body. We find, then, that the portion of the parasite interior to the 

 crab represents the skin of the larva, the external portion a genital 

 nucleus, which pierces its own investment and the integument of its 

 host. 



It is proposed to use in place of the term BMzocephala that of 

 Centrogonida, in reference to the dart-like organ of reproduction, and 

 to form of them an order distinct from the Cirripedia. 



On this communication Professor Lacaze-JDuthiers made some 

 remarks : * he insisted on the observations as demonstrating the 

 advantage and necessity of experiment in zoology. As to the in- 

 fectivity of young as compared with older crabs, he reminds us of the 

 differences between young and old human beings in their receptivity 

 of the poison of typhoid fever. The idea that the Sacculina 

 fixes itself to the interior of the crab must be given up, and the 

 animal not regarded as an ectoparasite, like a tick for example, but as 

 first entoparasitic and then forming a true hernia, developed within and 

 only passing outside the body to allow of the growth of some of its 

 organs. 



He concludes as follows : " If, in the eyes of some naturalists, 

 zoology is a purely descriptive science, it ought in many cases to be 

 experimental, so as to avoid the errors which are inseparable from a 

 study made at a limited point of time in the existence of organisms. 

 Our knowledge of development, which has been revealed to us by 

 experiment, will alone allow us to have an exact appreciation of 

 relations which are obscure and difficult of detection. It is for such 

 an object that we must distinguish between a zoology which is purely 

 descriptive and one which is experimental." 



Vermes. 



Classification of the Phyllodoceidse.t — G. Pruvot has especially 

 devoted his attention to the nervous system of these annelids, and 

 commences his note with an account of the arrangement found in 

 Phyllodoce laminosa. One of the results of the investigation is the 

 demonstration that the segment which carries the last tentacular cirrus 

 does not differ essentially from the normal setigerous segments. 



* Comptes Kendus, xcvii. (1883) pp. 1148-51. 

 t Ibid., pp. 1224-6. 



