INVERTEBRATA, CRYPTOftAMIAj MICROSCOPY, ETC. 813 



loped in some of the sterile polyps ; in all others the alternation is 

 complete. Though the phcuomeuou is of course associated with poly- 

 raorjjhism, it is not to be regarded as sim^ily due to it ; the limitation 

 of sexual reproduction to some of the similar individuals of a stock, 

 and the limitation of the gonojAore to the mature polyps, is to be 

 regarded as a process anterior to the truly secondary phenomena of 

 polymorphism. 



Orig^in of the Generative Cells in the Hydroida.* — Dr. Weiss- 

 man, in continuation of his researches t has discovered that the 

 male generative cells may arise in the coenosarc. Basing his result 

 on what he was able to observe in Plumtdaria echinidafa, we find 

 him saying that in the male, as well as in the female, gonaugia were 

 developed at points on the stalk thus ; a small group of ovarian or 

 seminal cells are, first of all, found in the endoderm, without any 

 indications whatever of any change in the perisarc or ectoderm. 

 Around this primitive reproductive organ there become developed a 

 special cap of cells of the ectoderm ; these cells become very remark- 

 ably and specially modified, are set at right angles to the supporting 

 membrane, and contain in the outer jjortion a fluid ; this, which is pro- 

 bably a secretion, causes an outswelling of the perisarc. In this last 

 a cleft gradually appears, which grows deeper and deeper ; through 

 this grow out the ectodermal and endodermal cells, covered by the 

 perisarc, and a gonangium is thus developed. 



The further generalization that in CorchjlopTiora the ovarian cells 

 arise in the trunk and not in the stalks of the hydranths, is supported 

 by the observation that the groups of ovarian cells are to be found in 

 quite young hydrauth-buds, before any tentacles are develojied, and 

 while the stalk is still quite short. Of course this mode of forming 

 generative cells is not found in all Hydroids (e. g. Tubularia) ; so 

 that with regard to the mode of origin of their generative cells, Hydroida 

 may be ranged in two series ; in one the generative cells arise in the 

 ccenosarc, and the so-called generative individuals are of secondary 

 origin ; in the other the generative individuals are primary, and it is 

 only in them that the generative cells arc developed ; the former are 

 Coenogenous, the latter Ulastogenous Hydroids. Further speculation 

 as to the phylogcnetic bearing of these observations is deferred for the 

 present. 



Porifera. 



Occurrence of Foreign Spicules in Sponges.t — In two cases, Mr. 

 S. O. Ridley has sliown this interesting and, to tlic working zoologist, 

 important phenomenon to have occurred. A species of Ciocalypfa, 

 characterized by a fibre which is almost wholly composed of long, 

 singly pointed ("acuate "") sjncules, with a simple rounded head and 

 sharp i)oiut, and by the almt)st absolute bareness of the outer or dermal 

 membrane in the natural condition, was found to contain in tlic latter, 

 in addition to tlic terminal spicules of the fibre proper, certain long 

 smooth spicules of about tlie same jinqioi-tiojis, but with a slight oval 



* ' Z(.<)1. Anzci;,'.,' iii. (1880) p. 'Mil. t ll>i<l., p. 220. 



X ' Jonrn. Linn. Hm:' (Z.>o).), xv. (1880) p. Hit. 



