NOTES ON THE ANATOMY OF DINOFHILUS. 59 



the male is said to tave neither penis nor vesiculae seminales, these 

 structures are found in D. tseniatus, which is probably closely allied 

 to D. gigas. 



I have no observations which explain the disappearance of D. 

 tseniatvs during the summer. It is, however, important to notice 

 that the eggs develop immediately after being laid. Small indi- 

 viduals were of common occurrence during- the early part of April, 

 although I did not succeed in finding the segmenting eggs till April 

 ] 6th ; the termination of my visit to Plymouth occurring a day or 

 two after that date, I have no observations worth recording on the 

 development. The eggs may be easily obtained by looking through 

 mud drawn by means of a siphon from the bottom of a rock-pool 

 which is inhabited by D. tseniatus. The general course of the deve- 

 lopment is apparently similar to that which has been described by 

 Korschelt in D. gyrociliatus {D. apatris) ; the embryo, as in this 

 species, acquiring most of its adult characters while still enclosed in 

 its vitelline membrane. The absence of any metamorphosis in Dino- 

 philus appears to me a noteworthy fact. It is perhaps a legitimate 

 inference, from the facts known with regard to Dinophilus, that a 

 Trochosphere stage is not to be expected in the ontogeny of this 

 animal, since in the persistence of the praeoral ring of cilia, and pro- 

 bably of the head-kidneys, and in the general characters of the ali- 

 mentary canal, the adult Dinophilus may be considered to remain in 

 a condition which is practically that of a Trochosphere. 



Postscript^ — I owe to the kindness of Dr. Norman the opportunity 

 of referring to the description which has been given by G. N. R. 

 Levinsen of Dinophilus caudatus, published in a paper which had 

 previously been inaccessible to me {Biclrag til KundsJcah om Gronlands 

 Turbellarienfauna, Vidensk. Meddel. fra den naturh. Foren. i Kjoben- 

 havn, 1879—1880). 



D. caudatus is identified by Levinsen with the Planaria caudata 

 of Fabricius (Fauna Groenlandica, 1780) and of 0. F. Miiller (Zool. 

 Danica), and, in the words of Fabricius, " Habitat stupenda multitu- 

 dine in confervis, et ulvis littoralibus, ssepe illas tegens." 



It resembles the species above described as D. tseniatus in the 

 division of the body into segments by deep constrictions of the skin, 

 in the form of the testes, and in the existence of a penis and of 

 vesiculge seminales, but is stated to be so well known that detailed 

 description is unnecessary ; it is, moreover, unfortunate that Levinsen 

 has published no figure of the species described by him. 



It appears to me quite possible that " D. tseniatus " is identical 

 with D. caudatus, but as the evidence on this point is quite incon- 

 clusive, I do not propose to withdraw, for the present at least, the 



