Studies on the Development of Larvai Nephridia. 491 



l)y Caldwell (3) that this animai is related to Bracbiopods, and in 

 a minor degree to Sipuneulids and possibly the Polyzoa. 



It is beyond the scope of the prcsent paper to euter iute a 

 discussion of tlie systematic positiou of Phoronis, especially as the 

 subjeet has been so thoroiighly revieAved in the recent papera of 

 De Öelys Longchamps (25 pag. 102) and Harmer (13 pag. 114). 



In many important memoirs, the nephridia bave been overlooked, 

 or bave received but scanty notice. While some find them opening 

 into the body cavity, others find them closed, and others again have 

 found no trace of them in the larva. Only within the last few years 

 bave tbey been the subjeet of careful examination. Goodrich (11) 

 was the first in 1903, to draw attention to the fact that the Actino- 

 trocha larva possessed nephridia furnished with solenocytes similar 

 to those of Polychaets. Since then several important papers bave 

 appeared. 



It is now evident that these organs are limited to a single pair, 

 situated in the third divisiou or trunk region of the larva, and that 

 they are closed, never opening into the body cavity or the primitive 

 space of the blastocoel in which they develop. They are in fact 

 typical larvai nephridia, furnished with solenocytes similar in all 

 respects to the solenocytes of Glycera and Phyllodoce among the 

 Polychaets. They belong to the category of true nephridia and as 

 such are qnite ditferent from the nephridia of Peripatus^ Pulmonata, 

 and some Chaetopods, which are diflferentiations of portions of 

 coelom and so modified genital ducts. The existence of the soleno- 

 cyte type of nephridium in the Actiuotrocha is a fact of some 

 morphological iniportance as it adds the Phoronidea to that class of 

 animals possessing nephridia of this primitive type. 



Wagener (26) in 1847, was the first to describe the nephridia 

 in the Actinotrocha larva thougb he misunderstood their nature. 

 He figured the solenocytes on the ends of the nephridial canals as 

 spermatozoon-like bodies, and considered the larva an adult form. 

 His figures are reraarkably good and all the main features of the 

 larva are shown. He draws the retractor muscle Strands running; 

 from the region of the Oesophagus to the nephridia very clearly, 

 structures which Ikeda has recently redescribed. For the Observation 

 of the nephridia, Actinotrocl/a branchiata, the form Wagener studied, 

 is very favourable. The nephridial canals are conspicuous and the 

 solenocytes attached to their ends very numerous. 



In 1883, thirty six years later, Caldwell (3) was the first to 



Mittheilungen a. d. Zool. Station zu Neapel. Ed. 17. 33 



