398 SUMMARY OF CURRENT RESEARCHES RELATING TO 



noticed in the case of two species of oyster, and in certain bony fishes. 

 From various facts observed he considers that they are not the male portion 

 of the egg-cell. The regular segmentation of the ovum is to be regarded 

 as resulting from its free life ; in most of the groujis of the animal kingdom 

 there are certain members whose eggs are not protected in any way, but 

 which float freely from the first, and there segment regularly; whereas eggs 

 which are protected either in capsules or in the parent's body and so on, 

 segment irregularly. The cause of this is mechanical, and is not so much 

 duo to the yolk present, as to gravity. 



Pelagic Annelids of the Gulf of Algiers.* — Dr. C. Viguier devotes 

 the second part of his essay on the lower animals of the Gulf of Algiers 

 to the pelagic Annelids, and to some general considerations on the con- 

 stitution of the members of their order. 



The pelagic Annelids may be divided into several groups ; some, like 

 the Ileteronereidao and the Syllida^, which exhibit no alternation of 

 generation, are for a short time only pelagic ; others are pelagic for the 

 whole course of their existence, but this is very brief, — they are the sexual 

 stolons of Syllids with alternation of generation. Tho Annelids that are 

 essentially pelagic all belong to tlie Alciopidfe or Phyllodoceida), with tho 

 latter of which may be associated Tomopteris and Sagittella. Of the forms 

 enumerated by the author, five — Maupasia ceeca g. et sp. n., lospilm 

 plmlacroides g. et sp. n., Alciope microcephala, Vanadis heterochseta, and 

 Amhlyosijllis algefnse — are new. 



The author is of opinion that the head of an Annelid is typically com- 

 posed of a single ring, formed directly fi'om the trochosphere ; this 

 trochosphere first buds off the pygidium, which grows and becomes seg- 

 mented. When the grooves which mark off the segments become apparent 

 tho first is seen to pass behind, or at least by the mouth ; in cases of 

 simple fissiparous reproduction, as e. g. in Syllis Jiumensis, one of the rings 

 of the primitive animal is very distinctly seen to be transformed into the 

 head of tho secondary individual, and alone to form its head. 



On the basis of the conclusions to which he arrives M. Viguier tries 

 to clear up the present confusion in the nomenclature of the parts of tho 

 Annelid ; if we put aside the branchite, we may say that each segment of a 

 free-swimming Annelid has only, on either side, a foot formed of a single 

 or of two projections (dorsal and ventral). This foot normally carries a 

 dorsal cirrus, which may be converted into an elytron, and a ventral cirrus 

 below. These cirri may become greatly developed, or, as well as tho 

 foot itself, may become more or less completely atrophied. The cirri of 

 the first or of the first few postcephalic rings often difi'er more or less 

 profoundly, in form and development, from those of the rings which 

 support them ; generally speaking, their importance is, in one animal, 

 in inverse proportion to that of the corresponding foot. He sees no reason 

 for a change of names, and refuses to make use of tho expressions tentacle 

 or tentacular cirrus ; where a note is necessary it is better to say that such 

 or such cirri (using their number in order) are tentacularized. 



The author commences his systematic account with the Phyllodoceidae 

 and the Alciopid^e, for between these families he is unable to draw any 

 absolute line of demarcation. Accounts are given of Pelagobia longocirrata, 

 which, unlike Greef, he does not place with the Syllidte ; of Maupasia caeca, 

 the representative of a new genus and species, but the generic and specific 

 characters are not technically distinguished in the account ; Hydrophanes 

 Krohnii ; Pontodora pelagica, which, again, the author removes from among 



* Arch. Zool. Expe'r. et Gcu., iv. (1S8G) pp. 317-112 (7 pis.). 



