438 



PROFESSOR LANKESTER. 



1. Anepitrochic — 



Bracliiolaria and Bipinnaria (of Asterids), some Gas- 

 tropods (?) 



2. Monepitrochic — 

 Torn aria. 



3. Polyepitrochic — 



Vermiform larva of Holothurians and Comatula. 

 c. — Ceplialotrochic (with suppression of the branchio- 

 troch) : 



1. Anepitrochic — 



Adult Rotifera, the trochosphere larva of Worms and 

 Molluscs, the veliger of Gastropods and Pteropods. 



2. Monepitrochic — 



The common two-girdled larva of Chaetopods. 



3. Polyepitrochic — 



The polytrochic larvae of Chaetopods, and other worms, 

 as also of Dentalium (Mollusc) and some Pteropods. 



IV. The Nephrtdia or segmental organs of the 

 Enterozoa. 



In all classes of the Enterozoa there are other openings, 

 usually small, into the cavity originally belonging to the 

 archenteron, besides the mouth and the anus. In those 

 Coelentera which foreshadow the ccelom by developing a 

 periaxial extension of the enterou or a perienteron, we find 

 such apertures especially associated with the rudimentary 

 ccelom. In the Actinozoa such apertures exist in the ten- 

 tacles or at the aboral pole. In some Ctenophora two 

 canals open from the as yet unspecialised cojlom to the ex- 

 terior bj two apertures placed at the aboral pole. 



When once the ccelom is accomplished as a cavity definitely 

 shut off from the "metenteron " — the name we now give to 

 what remains of the archenteron — its communications with 

 the exterior acquire a more important character. Whether 

 it be that the respiratory trees or that the orifices of the 

 ambulacral system in Echinoderma represent the communi- 

 cations established between the ccelom and the exterior in 

 the Coelonata, this appears certain, that in Rotifera, Flat- 

 worms, Gephyraea {not the genital ducts), Mollusca, in the 

 metameres of Chaetopoda, in the Vertcbrata, and even in 

 some Arthropoda, we have evidence of the existence of a 

 single pair of canals more or less highly modified by glan- 

 dular developments, which usually open by ciliated funnel- 

 like mouths into the ccelom at one end and directly to the 

 exterior in the neighbourhood of the anus, or into a cloacal 

 chamber, at their other end, thus placing the ca?lom in com- 

 munication with the exterior. 



