632 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Mr. Harmer considers that the true ganglion has been mistaken 

 for part of the generative apparatus, and describes it as being dumb- 

 bell-shaped and lying transversely across the intestine, as consisting 

 mesially of a fibrous commissural portion and of two lateral ganglia, 

 and as being altogether devoid of any central duct. The peripheral 

 nervous system is best examine 3. in living specimens, and the trans- 

 parent L. crassicauda is a most favourable species for investigation ; 

 it is described in detail. There is no striking objection to the idea 

 that the posterior sense-organs are homologous with the " osphradia" 

 of MoUusca, but it is more probable that they are merely specialized 

 sense-cells. 



After describing briefly the alimentary and muscular systems, the 

 author comes to the excretory organs, our knowledge of which is 

 exceedingly incomplete ; as described by Mr. Harmer they are seen to 

 differ markedly from those of the Brachiopoda, but to have the closest 

 similarity to the head-kidney of many Trochospheres. Dr. Meyer's 

 as yet unpublished drawings of the head-kidneys of various Annelid 

 larvae present a striking resemblance to Loxosoma in the number of 

 the excretory cells, in the relative size of the lumen in different parts 

 of the organ, and in the mode of termination in a flame-cell, as well 

 as in other points. The generative organs are next described, and 

 are stated to be " idiodinic." 



A careful account is given of the history of development, with 

 numerous references to the illustrative figures, which must be seen if 

 the account is to be fully understood ; this much, however, may be 

 here stated. The ova may be small, and be supplied with nutriment 

 from the glandular epithelium of the brood-pouch, or large, when 

 they take up the surrounding cells which play the part of a vitel- 

 larium ; the blastopore appears to form the permanent anus, and a 

 stomodoeum is developed anteriorly ; the greater part of the mesoblast 

 arises from two cells which are placed at the sides of the blastopore. 

 The so-called dorsal organ is of epiblastic and not of hypoblastic 

 origin, and is not a budding structure, but the supra-oesophageal 

 ganglion. Between the mouth and anus two epiblastic invaginations 

 appear, and, later on, fuse medianly ; they form the deeper part of 

 the vestibule, and, by the thickening of their floor, give rise to the 

 suboesophageal ganglia ; coming into contact with the " wings of the 

 crescent-shaped brain," they establish a complete circumoesophageal 

 nerve-ring. 



The Entoproctous Polyzoa, both larval and adult, are true 

 Trochospheres, with a ventral flexure of the alimentary canal, no 

 true body-cavity, and a pair of head-kidneys. The metamorphosis of 

 the Ectoprocta is a process of budding ; the Entoprocta have certain 

 affinities with Actinotrocha, while the affinity of the Polyzoa to the 

 Brachiopoda is more doubtful than to Phoronis. The nearest allies 

 of the Entoproctous Polyzoa are the Trochosphere larvae of Molluscs 

 and Chsetopods, and the adult Rotifera ; the Entoprocta are the most 

 archaic of the Polyzoa, but their relations to the rest are, as yet, 

 obscure. 



