48 C. F. JENKIN. 



one serious objection to this theory. The apical rays of the ordinary quadriradiates 

 would have to be bent down and straightened while the spicule turned round. The 

 shape of the apical ray in the chiactines suggests that this does occur, but it is difficult 

 to realise how an actually formed spicule can be altered in shape. 



Hair Spicules. — In many of the new species there occur long straight spicules 

 of extreme thinness, varying from about • 7 /x, to about 2 /a in diameter ; they are 

 called hair spicules. Their length is always difficult to determine. When they 

 occur in the oscular fringe the outer ends are usually broken ; when they occur in the 

 body -wall they are usually so crowded together that it is impossible to distinguish the 

 ends of individual spicules. It is probable that they often attain to lengths of 500 jx 

 or 1,000 fi. They often project from the body- wall with the ordinary thick oxea. The 

 hair spicules are usually omitted in the drawings of spicules, since their thickness is 

 too small to draw to scale and their length is uncertain. 



Flattened Spicules. — In two of the new species (Leucandra cirrata and 

 Megapogon crispatus) the large projecting oxea are marked near their distal ends by 

 curious flattened areas situated on the convex sides of the curved ends. Their 

 appearance might suggest that the spicule had come in contact with some tiat 

 obstruction which had diverted its growth and caused the mark. This, however, does 

 not seem to be possible, and no explanation of the origin of the marks has 

 been found. 



Ee PRODUCTION. 



Larvae similar to those of Sycon ciliatum were found in Tenthrenodes scotti and 

 Megapogon poUicaris. 



Ova of the ordinary type were found in Hypodictyon and in Achramorpha 

 glacialis. 



Duplicate ova of a remarkable type were found in Achramorpha nivalis and 

 Megapogon raripilus; no satisfactory explanation of their structure has been found. 

 They were in large numbers in three specimens of Achramorpha nivalis ; the best 

 preparations were made from one of the specimens which had been fixed in osmic acid. 

 None of the specimens of Megapogon raripilus were as well fixed, nor could the 

 structure of the ova be made out so satisfactorily ; it appears to differ slightly from 

 that of Achramorpha nivalis. 



The following description applies to the ova of Achramorpha nivalis: — 



Each ovum (Fig. 110) appears to be made up of two unequal parts; the 

 larger part {a) is very similar to the ordinary large ovum cell and contains a large 

 transparent nucleus {b) and small strongly staining nucleolus (c) ; the smaller part 

 appears to be a multicellular structure, consisting of a large inner cell surrounded by a 

 sheath of small cells {d) ; (but it is possible that it may be a single cell, the central 

 portion {g) being the nucleus). The inner cell {g) contains two structures ; one (A) 

 strongly staining like the nucleolus of the larger part, the other a hyaline sphere {i) 



